Override notification related interface from content

There are four methods in content browser client which are for
client to implement to support web notification.
Override those apis with empty function bodies first.
[Android] Implement W3C WebNotification API

W3C web notification API is defined at http://www.w3.org/TR/notifications/.
On Android, web notifications are well matched to system notifications.
To invoke js callbacks when system notification got clicked or canceled,
two pendingIntents are binded to the notification.
Since Android only keeps one pendingIntent for specified Context/Class/Category,
the unique id of the notification is used as the Category of the pendingIntents.

Platforms other than Android keeps empty implementaion for notification related
interfaces.

TEST=XWalkCoreTest org.xwalk.core.xwview.test.WebNotificationTest
BUG=https://crosswalk-project.org/jira/browse/XWALK-94
Fix build for Mac.

The sync of gyp_xwalk with gyp_chromium 34 disabled the circular dependency check for
all platforms but Mac. Upstream doesn't have circular problems on the Mac platform
but we do so we need to skip the circular check for now. I also put back the TODO as
it was.
[Runtime] Fix Tizen IVI build error for PR#1593.
IVI buildbot reports error:
'xwalk::application_widget_keys::kIcon128Key' has a previous declaration
as 'const char xwalk::application_widget_keys::kIcon128Key []'

This PR fix above error.
Merge pull request #1470 from wang16/w3c_notification

[Android] Implement W3C notification API
DEPS.xwalk: Roll chromium-crosswalk to 954426

954426: Merge pull request #131 from yinli/volume-webaudio-trunk
[Android] [Backport] Volume is too low when playing audio through WebAud...
Revert "[Android] Add eclipse build support for xwalk_core_library"

This reverts commit 3f155dfc89e39dbde7adeecd4a1fa139fec88789.
Revert "[Android] Fix incorrect res ids for apps using cordova xwalk"

This reverts commit a2ece240670d66509f3b4eafa55ced7172f0f23f.
[Android] Determine id for resources in chromium at runtime

In chromium, there are two java targets containing resources.
They are org.chromium.content.R and org.chromium.ui.R. The
R.java of these two package in chromium repo are just a
declaration with no ids specified.

In chromium's gyp system, it is handled well to make sure the
ids are unique for each resource.

If xwalk core is used as an Android library project, all the
resources will be only counted in org.xwalk.core.R. Previously,
we added an additional step running as pre-compile to copy
org.xwalk.core.R to org.chromium.content and org.chromium.ui to
make the ids correct.

Now we want to expose a set of embedding API based on xwalk core
library, which will be an Android library project used by multiple
projects. The original way is not appropriate any more.

The new solution is to set the ids at runtime by using java
reflection to iterate over chromium resources.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1042
[Android] Clean everything in xwalk_core_library folder for each build

Otherwise, there may remain some legacy files even it's removed
from the source tree.
Merge pull request #1641 from yinli/roll_deps_to_webaudio_volume_fix

DEPS.xwalk: Roll chromium-crosswalk to 954426
Merge pull request #1639 from darktears/mac-build-fix

Fix build for Mac.
Merge pull request #1640 from shaochangbin/fix_build_error

[Runtime][IVI] Fix Tizen IVI build error by PR#1593.
Merge pull request #1637 from wang16/core_library_refine

[Android] Determine id for resources in chromium at runtime