gpu: Fix some context lost marking glitches+leaks and add UMA stats

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 61fd8409dfa26dbbb2a2e52266667ea9a2d9180f..f5d5a381c046128f958e03728d514b12620585d0 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -1294,7 +1294,7 @@ RenderThreadImpl::GetGpuFactories() {
                   GURL("chrome://gpu/RenderThreadImpl::GetGpuVDAContext3D"),
                   WebGraphicsContext3DCommandBufferImpl::SharedMemoryLimits(),
                   NULL)),
-          "GPU-VideoAccelerator-Offscreen");
+          GPU_VIDEO_ACCELERATOR_CONTEXT);
     }
   }
   if (gpu_va_context_provider_.get()) {
@@ -1331,12 +1331,12 @@ RenderThreadImpl::SharedMainThreadContextProvider() {
     if (SynchronousCompositorFactory* factory =
             SynchronousCompositorFactory::GetInstance()) {
       shared_main_thread_contexts_ = factory->CreateOffscreenContextProvider(
-          GetOffscreenAttribs(), "Offscreen-MainThread");
+          GetOffscreenAttribs(), RENDERER_MAINTHREAD_CONTEXT);
     }
 #endif
     if (!shared_main_thread_contexts_.get()) {
       shared_main_thread_contexts_ = ContextProviderCommandBuffer::Create(
-          CreateOffscreenContext3d(), "Offscreen-MainThread");
+          CreateOffscreenContext3d(), RENDERER_MAINTHREAD_CONTEXT);
     }
     if (shared_main_thread_contexts_.get() &&
         !shared_main_thread_contexts_->BindToCurrentThread())