[Android] Enable tracing on XWalkCoreShell

Add an Intent receiver to XWalkCoreShell for tracing event recording.

How to use it:
1. Launch XWalkCoreShell on Android device
2. Start and stop tracing recoding by running the commands on host machine:
   # adb shell am broadcast -a org.xwalk.core.xwview.shell.GPU_PROFILER_START -e file /sdcard/Download/trace.txt
   # adb shell am broadcast -a org.xwalk.core.xwview.shell.GPU_PROFILER_STOP
3. Run 'adb pull /sdcard/Download/trace.txt' to download the trace.txt to host machine
4. Open about:tracing in Chrome browser on host machine and load the trace.txt

BUG=https://crosswalk-project.org/jira/browse/XWALK-795
Merge pull request #1433 from hmin/tracing

[Android] Enable tracing on XWalkCoreShell