Added preliminary support for tile rasterization with Ganesh

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 10014f8b89d9ab4d1fb9805210e8ac5176652a2a..f34eb18f6644fed9f988c7139294e1588d856805 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -168,6 +168,7 @@ GLRenderer::GLRenderer(RendererClient* client,
       is_backbuffer_discarded_(false),
       visible_(true),
       is_scissor_enabled_(false),
+      scissor_rect_needs_reset_(true),
       stencil_shadow_(false),
       blend_shadow_(false),
       highp_threshold_min_(highp_threshold_min),
@@ -2486,7 +2487,7 @@ void GLRenderer::SetScissorTestRect(gfx::Rect scissor_rect) {
 
   // Don't unnecessarily ask the context to change the scissor, because it
   // may cause undesired GPU pipeline flushes.
-  if (scissor_rect == scissor_rect_)
+  if (scissor_rect == scissor_rect_ && !scissor_rect_needs_reset_)

[reveman, 2013/11/24 21:56:57]

can you explain why we need this now but not before?

[slavi, 2013/11/25 23:13:14]

Ganesh and the GlRendeder are sharing the GL state. Also, Ganesh assumes that
the state will be the same as it was last left. This fixes such a state bug
having to do which scissoring. I believe there's another bug lurking having to
do with GL blend state.

[enne (OOO), 2013/11/25 23:14:10]

Yeah, this looks like it should be a separate patch.  Could you just set the
scissor_rect_ to empty instead of adding a separate boolean?  Also, should
scissor_rect_ be renamed scissor_rect_shadow_ to match the other shadowing
variables and make it more clear?

[slavi, 2013/11/25 23:22:52]

Ok. I'll prepare it as a separate patch.

     return;
 
   scissor_rect_ = scissor_rect;
@@ -2496,6 +2497,8 @@ void GLRenderer::SetScissorTestRect(gfx::Rect scissor_rect) {
                         scissor_rect.y(),
                         scissor_rect.width(),
                         scissor_rect.height()));
+
+  scissor_rect_needs_reset_ = false;
 }
 
 void GLRenderer::SetDrawViewport(gfx::Rect window_space_viewport) {
@@ -2946,6 +2949,7 @@ void GLRenderer::ReinitializeGLState() {
   // Make sure scissoring starts as disabled.
   is_scissor_enabled_ = false;
   GLC(context_, context_->disable(GL_SCISSOR_TEST));
+  scissor_rect_needs_reset_ = true;
 }
 
 bool GLRenderer::CanUseSkiaGPUBackend() const {