Make sure frame buffer 0 is bound before calling GL functor

Make sure view port and frame buffer are set to the correct values
before calling GL functor (WebView) draw.
Improve correctness for stencil clip by doing a second flush that
guarantees the stencil clear will be executed after draw commands.

Bug: 79619253
Test: XFINITY Connect app draws correctly
Change-Id: Ieb3d0d70caf0469b6393e6287f8529cd86519301