cc: Add threaded GPU rasterization.

content/browser/android/in_process/synchronous_compositor_impl.cc

Index: content/browser/android/in_process/synchronous_compositor_impl.cc
diff --git a/content/browser/android/in_process/synchronous_compositor_impl.cc b/content/browser/android/in_process/synchronous_compositor_impl.cc
index e76b36b85be6b0e5698c9c5d4e4b12d82f50ad7a..fe7a1326c9c8ce6ab6bd2c7c585a1cdde7c5327a 100644
--- a/content/browser/android/in_process/synchronous_compositor_impl.cc
+++ b/content/browser/android/in_process/synchronous_compositor_impl.cc
@@ -154,7 +154,11 @@ bool SynchronousCompositorImpl::InitializeHwDraw() {
   scoped_refptr<cc::ContextProvider> onscreen_context =
       g_factory.Get().CreateOnscreenContextProviderForCompositorThread();
 
-  bool success = output_surface_->InitializeHwDraw(onscreen_context);
+  scoped_refptr<cc::ContextProvider> worker_context =
+      g_factory.Get().CreateOnscreenContextProviderForCompositorThread();

[boliu, 2015/02/13 18:04:05]

Is it possible/safe to key this off of a command line switch? For webview,
creating and destroying context happens as normal part of operation, not just on
start up/tear down/error. Creating a context is pretty expensive, so it could
have perf impact.

Also just rename the method to CreateContextProviderForCompositor.

[vmiura, 2015/02/13 19:52:34]

We need it whenever GPU rasterization is enabled.  Is it safe to check something
like Content::IsGpuRasterizationEnabled() here?.
Done.

[boliu, 2015/02/13 20:25:52]

Oh I thought the new context will only be used with
--enable-threaded-gpu-rasterization. If it's needed for ganesh in general, then
I don't think it's worth it.

I think the answer to IsGpuRasterizationEnabled is yes. It is safe since it's
just reading a bunch of command line switches.

+
+  bool success =
+      output_surface_->InitializeHwDraw(onscreen_context, worker_context);
 
   if (success)
     g_factory.Get().CompositorInitializedHardwareDraw();