[Extensions] Add command line switch xwalk-extension-cmd-prefix

This will prepend the contents of this flag to the command line
when starting extension process, it works as same as the switch
"--renderer-cmd-prefix", could be useful if we need to debug
the extension process at its very beginning.
Useful values might be "valgrind" or "xterm -e gdb --args".

Also modified the child path flag which is used to retrieve the
child process' execution file according to the extension command
line prefix on linux. In most cases we need to use CHILD_ALLOW_SELF
to exec child process from /proc/self/exe to prevent chromium's
autoupdate feature to change the file out from underneath; For the
case of xwalk-extension-cmd-prefix, as we suppose to override the
command line to load the app directly, we need to use CHILD_NORMAL
to exec child process from its real app path.
xwalk.gyp: Fix building for Android without webkit debug symbols

Fix missing symbols at linker stage when building with option
'remove_webcore_debug_symbols' by adding the required dependencies
to the 'xwalk_runtime' target.
dbus_manager_tizen: Remove useless glib include
xwalk.gyp: Explicitly add jsoncpp dependency

The lack of this dependency was generating error, required by
ScreenOrientationExtension.
runtime/browser: Fix header file changes

Offending CL:
https://codereview.chromium.org/174803002
Merge pull request #1793 from r0b5t4/foo

xwalk.gyp: Fix building for Android without webkit debug symbols
Merge pull request #1794 from tiagovignatti/for-upstream

For upstream
Bump version to 6.34.115.0
[Tizen] packaging: explicitly disable GNOME Keyring support.

gnome-keyring isn't packaged for Tizen, and we are not interested in using
it at the moment anyway.

While support for it is disabled by default when Aura is used in M34, this
is not the case anymore since Chromium r251992 (part of M35). Prepare for it
by explicitly disabling the support in master so that the actual commit that
moves to M35 in crosswalk is smaller.
Merge pull request #1795 from rakuco/tizen-no-gnome-keyring

[Tizen] packaging: explicitly disable GNOME Keyring support.
Bump version to 6.34.116.0
Merge pull request #1780 from jondong/master

[Extensions] Add command line switch xwalk-extension-cmd-prefix
[Android] Support the default_orientation in packaging tool.

Since the filed of 'default_orientation' is added in current W3C
manifest, this pull request adds the corresponding support in packaging
tool including manifest parser and command line option handler.

BUG=XWALK-1267