[Android] Implement the http authentication in xwalk default client.

  The implementation is to provide the http anthentication
funtions to support the authentication requirement of some
web site related to username and password, covering the
following:
1 Import and implement a general class of HttpAuthDatabase
  to support common http authentication database interfaces.
  This class imports the android sqlite database to handle
  the username and password data on demand.
2 In default xwalk client, implement the method of
  setHttpAuthUsernamePassword() by calling the related method
  of HttpAuthenDatabase instance to set the username and password.
3 In default xwalk client, implement the method of
  getHttpAuthUsernamePassword() by calling the related method
  of HttpAuthenDatabase instance to query the username and password.

BUG=#784, #787
[Android] Refine the xwalk_core_test_apk target

This fix is to refine the test target to make it more cleaner to add
HTML testing file as apk asset file. Right now, when adding a new HTML
file for testing, you just need to update the 'sources' list without
adding a new entry item in 'copies' list.
[Tizen] Fix Glib assertion due to appcore_context.

This patch get rid of following log:
[ERROR:browser_main_loop.cc(228)] GLib: g_source_destroy: assertion `source != NULL' failed

AppcoreContext::Initialize() fails when we launch xwalk in the shell. e.g. > xwalk
It is because appcore_init() can success only if registered application (e.g.
web applications) is launched.

This patch handles the exception that AppcoreContext::Initialize() fails.
Fix build for Windows.

Windows switched to Aura therefore we need to remove the old code
path and use the generic method to access the title. The compilation
failure was due to the fact that NativeWindow type is not anymore
a HWND.

BUG=936
Bump version to 2.31.21.0
Merge pull request #931 from hmin/refine-test-target

[Android] Refine the xwalk_core_test_apk target
[Android] Remove the wrong dependence in runtime client test apk.

This patch will resolve the issue about wrong dependence in the runtime
client test apk.
In file CrossPackageWrapper.java, the constructor function "CrossPackageWrapper()"
has the judgement about the class loaded. In shared mode, the core shell is not
needed for the runtime client test shell.

BUG=#916
Merge pull request #917 from wuhengzhi/shared_issue

[Android] Remove the wrong dependence in runtime client test apk.
[Android] Create the XWalkRenderViewExt object.

XWalkRenderViewExt is a class that handles several IPCs from the class
XWalkRenderViewHostExt. To make it work, an object of XWalkRenderViewExt
must be created first.
[Android] Fix #705 to support multiple frames for extension mechanism

When there are multiple frames in one page, extension instance will
be created for each frame. But as internal WebFrame is not exposed
in Java side, there is no way for Java side to identify which
instance to send message. This patch exposed instanceID up to Java
side when it receives message which can be used to identify the
target instance when post message to JavaScript side. What's more
a new interface "broadcastMessage" was added to meet the requirement
that Java side may need to broadcast message to all exiting instances.

Changed interfaces for Java extension:
1. postMessage(String msg) -> postMessage(int instanceID, String msg)
2. onMessage(String msg)   -> onMessage(int instanceID, String msg)
3. onSyncMessage(String msg) -> onSyncMessage(int instanceID, String msg)
4. new added: broadcastMessage(String msg)

BUG=#705
[Android] Fix incorrect res ids for apps using cordova xwalk

Cordova xwalk container is using xwalk core library as an
Android library project.
For Android library project, it will generate the R.java for
it when building the project depends on it (Let's call it app
project). But the R.class will be excluded when generating
classes.jar. Then the resources within both app and library will
be put together to generate R.java for both app and library
package, it is to make sure the ids for them will not be conflicted.

Meanwhile, the dependencies for android java target in gyp system
is not the same. It breaks down the ant tasks and customized them
in very complicated way, each java src target which contains resources
will produce an R.txt which has allocated ids in it. The project
depends on it will generate R.java based on that to avoid conflicts.

The two things can't work together, but the command line interface
cordova container provides to developer should not be changed.

The solution is here,
Take all resources within xwalk core library as resrouces for library.
An R.java will generated at code-gen step for them. This patch will
overwrite the pre-compile step between code-gen and compile.
The step will copy R.java for core library to package
org.chromium.content and org.chromium.ui, as well as replace the
determined id values in it with the references to org.xwalk.core.R.

BUG=https://github.com/crosswalk-project/crosswalk/issues/862
[Android] Fix text selection menu being auto-dismissed in some cases

In previous xwalk implementation, the load operation will trigger
a pair of clear/request focus operation. Which makes the text selection
context menu hide immediately after it shows sometimes.

The fix is to only request focus when loading url.
Merge pull request #950 from wang16/cordova_txt_sel

[Android] Fix text selection menu being auto-dismissed in some cases
Merge pull request #935 from ds-hwang/appcorebug

[Tizen] Fix Glib assertion due to appcore_context.
Merge pull request #907 from DonnaWuDongxia/multi-frame-support-in-one

[Android] Fix #705 to support multiple frames for extension mechanism
[Android] Return the correct context for external extensions

The previous implementation returns the context of runtime side which is
a context for library package. This is true for internal extensions. However,
for external extensions, the context should be the same as the activity
because they're inside of runtime client. This is to fix the issue to return
the activity as the context for external extensions.

BUG=#777
[Android] Add one interface to set whether to load external extensions.

For some usage scenarios, external extensions are not needed
because it has its own plugin or extension mechanism. Hence here a new
method is used to enable/disable the mechanism to load external extensions.

BUG=#948
[Android] Define the class XWalkRuntimeViewProvider as an interface.

It's an abstract class and some shared implementations are included
and will be used by inherited classes. However, xwalk core library needs
an interface which will be implemented by the container.
To meet this requirement, split this class into two: one interface containing
all methods and the base class to contain some shared implementations like
managing extensions.
Merge pull request #938 from darktears/win-test-fix

Fix build for Windows.
[Windows] Remove uneeded files after the move to Aura.

We don't need these files as we moved to Aura. They are excluded
from the build upstream.