Plumb through EGL_NV_post_sub_buffer and GLX_MESA_copy_sub_buffer.

content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc

Index: content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc
diff --git a/content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc b/content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc
index 6564f1c07c055dc0425a7632627e1cdf78a8297f..9d0e3ed407c2b2f256a317313656776aa777361a 100644
--- a/content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc
+++ b/content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc
@@ -292,6 +292,12 @@ void WebGraphicsContext3DCommandBufferImpl::prepareTexture() {
 #endif
 }
 
+void WebGraphicsContext3DCommandBufferImpl::postSubBufferCHROMIUM(
+    int x, int y, int width, int height) {
+  gl_->PostSubBufferCHROMIUM(x, y, width, height);
+  // FIXME(backer): Do we need a flush?
+}
+
 void WebGraphicsContext3DCommandBufferImpl::reshape(int width, int height) {
   cached_width_ = width;
   cached_height_ = height;