Skia: GPU backend enhancement for canvas2D.

Improve browser performance for canvas2D, we adopted skia-gpu backend.
Add a switch to turn on GR_STATIC_RECT_VB flag, which improve the performance.

Change-Id: I41059c745ef4ee727cfbb5471b697bbfae238015
Author: Kangyuan Shu <kangyuan.shu@intel.com>
Singed-off-by: Shuo Gao <shuo.gao@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 26567

Conflicts:
	Android.mk