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

content/browser/gpu/compositor_util.cc

Index: content/browser/gpu/compositor_util.cc
diff --git a/content/browser/gpu/compositor_util.cc b/content/browser/gpu/compositor_util.cc
index 0f01ec83812eb7d368c5fb6af2011e5570ea2dd9..9606eb56756506d28b3b9df1bf77fabe5f3cd933 100644
--- a/content/browser/gpu/compositor_util.cc
+++ b/content/browser/gpu/compositor_util.cc
@@ -292,6 +292,21 @@ bool IsForceGpuRasterizationEnabled() {
   return command_line.HasSwitch(switches::kForceGpuRasterization);
 }
 
+bool IsThreadedGpuRasterizationEnabled() {
+  if (!IsImplSidePaintingEnabled())
+    return false;
+
+  const base::CommandLine& command_line =
+      *base::CommandLine::ForCurrentProcess();
+
+  if (command_line.HasSwitch(switches::kDisableThreadedGpuRasterization))
+    return false;
+  if (command_line.HasSwitch(switches::kEnableThreadedGpuRasterization))
+    return true;
+
+  return false;
+}
+
 bool UseSurfacesEnabled() {
 #if defined(OS_ANDROID)
   return false;