gpu: Add flag for enabling asynchronous worker context.

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index 727717eea390b55c1de71d01668d41766d9afbcc..b25a36d8c1ef11ded3466863ab8fe334d3526cf8 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -775,12 +775,19 @@ std::unique_ptr<cc::OutputSurface> RenderWidget::CreateOutputSurface(
 
     bool automatic_flushes = false;
 
-    // The compositor context shares resources with the worker context.
+    // The compositor context shares resources with the worker context unless
+    // the worker is async.
+    ContextProviderCommandBuffer* share_context = worker_context_provider.get();
+    if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+            switches::kEnableGpuAsyncWorkerContext)) {
+      share_context = nullptr;
+    }
     context_provider = new ContextProviderCommandBuffer(
         base::WrapUnique(new content::WebGraphicsContext3DCommandBufferImpl(
             gpu::kNullSurfaceHandle, GetURLForGraphicsContext3D(),
             std::move(gpu_channel_host), gfx::PreferIntegratedGpu,
-            automatic_flushes)),
+            automatic_flushes, gpu::GPU_STREAM_DEFAULT,
+            gpu::GpuStreamPriority::NORMAL)),
         limits, attributes, worker_context_provider.get(),
         command_buffer_metrics::RENDER_COMPOSITOR_CONTEXT);