Reset GL state before copying RenderPassDrawQuads to CALayers.

cc/output/gl_renderer.cc

Index: cc/output/gl_renderer.cc
diff --git a/cc/output/gl_renderer.cc b/cc/output/gl_renderer.cc
index f8d70c4ddb85012371f11a05db47a70bd3375a6f..fb1ee183c2a86feaffa6e4c294cb047b98c25384 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -3864,6 +3864,9 @@ void GLRenderer::CopyRenderPassDrawQuadToOverlayResource(
     Resource** resource,
     DrawingFrame* external_frame,
     gfx::RectF* new_bounds) {
+  // Don't carry over any GL state from previous RenderPass draw operations.
+  ReinitializeGLState();

[ericrk, 2016/08/24 19:04:50]

This makes sense - so the state was just left over from previous rendering?

Also, I wonder if we should do this higher up the chain (in ScheduleCALayers?)
to avoid re-setting this state unnecessarily a bunch of times?

[erikchen, 2016/08/24 20:04:36]

Yup. Unfortunately, GLRenderer is very stateful.
I considered that. Most of the time, this function never gets called, so that
would be unnecessary. We could add yet more logic to ScheduleCALayers to only
call this once, and only right before CopyRenderPassDrawQuadToOverlayResource().
Then again, we're assuming that none of the drawing operations from this
function modify state that needs to be reset between successive calls to this
function. [This is currently true, but there's no reason it has to be true going
forward.] Overall, reinitializing state here seemed like a good choice,
especially given that the overhead is minimal compared to the cost of actual
drawing operations.

+
   ScopedResource* contents_texture =
       render_pass_textures_[ca_layer_overlay->rpdq->render_pass_id].get();
   DCHECK(contents_texture);
@@ -3967,11 +3970,7 @@ void GLRenderer::CopyRenderPassDrawQuadToOverlayResource(
 
   // Clear to 0 to ensure the background is transparent.
   gl_->ClearColor(0, 0, 0, 0);
-  if (is_scissor_enabled_)
-    gl_->Disable(GL_SCISSOR_TEST);
   gl_->Clear(GL_COLOR_BUFFER_BIT);
-  if (is_scissor_enabled_)
-    gl_->Enable(GL_SCISSOR_TEST);
 
   UpdateRPDQTexturesForSampling(&params);
   UpdateRPDQBlendMode(&params);