Add a command-line flag to enable threaded GPU rasterization.

content/browser/gpu/compositor_util.h

Index: content/browser/gpu/compositor_util.h
diff --git a/content/browser/gpu/compositor_util.h b/content/browser/gpu/compositor_util.h
index 6266f36e1cbeefc7225835c72dcdef3e3f535da1..16dca45c45ad6f50fb522aab32067d3f8209e3f3 100644
--- a/content/browser/gpu/compositor_util.h
+++ b/content/browser/gpu/compositor_util.h
@@ -42,6 +42,10 @@ CONTENT_EXPORT int GpuRasterizationMSAASampleCount();
 // Returns true if force-gpu-rasterization is on (via flags) for the renderer.
 CONTENT_EXPORT bool IsForceGpuRasterizationEnabled();
 
+// Returns true if threaded GPU rasterization is on (via flags) for the
+// renderer.
+CONTENT_EXPORT bool IsThreadedGpuRasterizationEnabled();
+
 // Returns the number of raster threads to use for compositing.
 CONTENT_EXPORT int NumberOfRendererRasterThreads();