Plumb composition character bounds for Android 5.0
This is a groundwork to support CursorAnchorInfo API for Android 5.0. No user visible change is intended with this CL.
With this CL, ImeCompositionRangeChanged event will be routed from the renderer to the browser in Android 5.0 and above. The underlying functionality has been widely used in desktop OSes for years. There should be no performance impact for existing in Android 4.4 and prior version. Performance impact on Android 5.0 devices will be tracked as Issue 427090. Actual plumbing from native to Java layer will be handled in subsequent CLs.
TEST=Manually done on Nexus 7 Build/LPX13D