cc: Stop using magic numbers to detect if we can use partial updates.

cc/trees/layer_tree_host.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include <algorithm>
 #include <stack>
 
 #include "base/bind.h"
@@ skipping 1100 matching lines @@
   }
 }
 
 void LayerTreeHost::RateLimit() {
   // Force a no-op command on the compositor context, so that any ratelimiting
   // commands will wait for the compositing context, and therefore for the
   // SwapBuffers.
   proxy_->ForceSerializeOnSwapBuffers();
 }
 
+bool LayerTreeHost::AlwaysUsePartialTextureUpdates() {
+  if (!proxy_->GetRendererCapabilities().allow_partial_texture_updates)
+    return false;
+  return !proxy_->HasImplThread();
+}
+
 bool LayerTreeHost::RequestPartialTextureUpdate() {
   if (partial_texture_update_requests_ >= settings_.max_partial_texture_updates)
     return false;
 
   partial_texture_update_requests_++;
   return true;
 }
 
 void LayerTreeHost::SetDeviceScaleFactor(float device_scale_factor) {
   if (device_scale_factor == device_scale_factor_)
@@ skipping 105 matching lines @@
 void LayerTreeHost::RegisterViewportLayers(
     scoped_refptr<Layer> page_scale_layer,
     scoped_refptr<Layer> inner_viewport_scroll_layer,
     scoped_refptr<Layer> outer_viewport_scroll_layer) {
   page_scale_layer_ = page_scale_layer;
   inner_viewport_scroll_layer_ = inner_viewport_scroll_layer;
   outer_viewport_scroll_layer_ = outer_viewport_scroll_layer;
 }
 
 }  // namespace cc