Implement Discard and EnsureBackbufferCHROMIUM using command buffer instead of IPC.

content/common/gpu/client/webgraphicscontext3d_command_buffer_impl.cc

Index: content/common/gpu/client/webgraphicscontext3d_command_buffer_impl.cc
diff --git a/content/common/gpu/client/webgraphicscontext3d_command_buffer_impl.cc b/content/common/gpu/client/webgraphicscontext3d_command_buffer_impl.cc
index 062c39204ac326aa6fbfa11f4b0d6bb4b6df54dc..6eeaaf66950432ad61948fc5d74900fbb824d568 100644
--- a/content/common/gpu/client/webgraphicscontext3d_command_buffer_impl.cc
+++ b/content/common/gpu/client/webgraphicscontext3d_command_buffer_impl.cc
@@ -456,13 +456,11 @@ void WebGraphicsContext3DCommandBufferImpl::setVisibilityCHROMIUM(
 
 void WebGraphicsContext3DCommandBufferImpl::discardFramebufferEXT(
     WGC3Denum target, WGC3Dsizei numAttachments, const WGC3Denum* attachments) {
-  gl_->Flush();
-  context_->DiscardBackbuffer();
+  gl_->DiscardBackbufferCHROMIUM();
 }
 
 void WebGraphicsContext3DCommandBufferImpl::ensureFramebufferCHROMIUM() {
-  gl_->Flush();
-  context_->EnsureBackbuffer();
+  gl_->EnsureBackbufferCHROMIUM();
 }
 
 void WebGraphicsContext3DCommandBufferImpl::
@@ -1269,4 +1267,3 @@ void WebGraphicsContext3DCommandBufferImpl::OnErrorMessage(
     error_message_callback_->onErrorMessage(str, id);
   }
 }
-