Adding ANGLE systrace support

Plumb ANGLE systrace support into Android by setting ANGLE
PlatformMethods struct to required function pointers used by built-in
ANGLE tracing macros.

This includes "#define ATRACE_TAG ATRACE_TAG_GRAPHICS" so that these
markers will fall under the "gfx" class of systrace.

This requires mirroring new header, Platform.h, from ANGLE.

Added AnglePlatformImpl class with static functions that are assigned
into PlatformMethods struct that's passed to ANGLE. This lives in new
egl_angle_platform.h/cpp files. Since we're moving to ANGLE as default
long-term I think it makes sense to have this file live in EGL dir
where I put it.

Currently only defining the functions that we needs to support systrace
through existing ANGLE PlatformMethods. Could potentially expand this
to define more.

Test: build and flash device, run app w/ ANGLE enabled, systrace
Change-Id: I3f0812e8a7554768bbecc3e94feac6559ce17bb2
(cherry picked from commit b032494f6ce813323e79a55a0caa216997fe6a5d)