Aura: Support --enable-partial-swap with --composite-to-mailbox

content/renderer/gpu/mailbox_output_surface.cc

Index: content/renderer/gpu/mailbox_output_surface.cc
diff --git a/content/renderer/gpu/mailbox_output_surface.cc b/content/renderer/gpu/mailbox_output_surface.cc
index 80e7ed22d7c61cc91fec4cd5b96f345d7bf0182a..8af117d2aa453354bdc95244273de237cfc03254 100644
--- a/content/renderer/gpu/mailbox_output_surface.cc
+++ b/content/renderer/gpu/mailbox_output_surface.cc
@@ -163,10 +163,6 @@ void MailboxOutputSurface::OnSwapAck(const cc::CompositorFrameAck& ack) {
 
 void MailboxOutputSurface::SwapBuffers(cc::CompositorFrame* frame) {
   DCHECK(frame->gl_frame_data);
-  DCHECK(frame->gl_frame_data->sub_buffer_rect.size() ==
-         frame->gl_frame_data->size)
-      << "Partial swap not supported with composite-to-mailbox yet.";
-
   DCHECK(!surface_size_.IsEmpty());
   DCHECK(surface_size_ == current_backing_.size);
   DCHECK(frame->gl_frame_data->size == current_backing_.size);