Add a command-line flag to set GPU rasterization multisampling.

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 f94d20ca2f8e39b9f4197116c160b211840ed806..6266f36e1cbeefc7225835c72dcdef3e3f535da1 100644
--- a/content/browser/gpu/compositor_util.h
+++ b/content/browser/gpu/compositor_util.h
@@ -35,6 +35,10 @@ CONTENT_EXPORT bool IsZeroCopyUploadEnabled();
 // Returns true if gpu rasterization is on (via flags) for the renderer.
 CONTENT_EXPORT bool IsGpuRasterizationEnabled();
 
+// Returns the number of multisample antialiasing samples (via flags) for
+// GPU rasterization.
+CONTENT_EXPORT int GpuRasterizationMSAASampleCount();
+
 // Returns true if force-gpu-rasterization is on (via flags) for the renderer.
 CONTENT_EXPORT bool IsForceGpuRasterizationEnabled();