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

cc/layers/tiled_layer.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/layers/tiled_layer.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "base/auto_reset.h"
@@ skipping 423 matching lines @@
     for (int i = left; i <= right; ++i) {
       UpdatableTile* tile = TileAt(i, j);
       DCHECK(tile);  // Did SetTexturePriorites get skipped?
                      // TODO(enne): This should not ever be null.
       if (!tile)
         continue;
       if (tile->occluded && !ignore_occlusions)
         continue;
       // TODO(reveman): Decide if partial update should be allowed based on cost
       // of update. https://bugs.webkit.org/show_bug.cgi?id=77376
-      if (tile->is_dirty() && layer_tree_host() &&
-          layer_tree_host()->buffered_updates()) {
+      if (tile->is_dirty() &&
+          !layer_tree_host()->AlwaysUsePartialTextureUpdates()) {
         // If we get a partial update, we use the same texture, otherwise return
         // the current texture backing, so we don't update visible textures
         // non-atomically.  If the current backing is in-use, it won't be
         // deleted until after the commit as the texture manager will not allow
         // deletion or recycling of in-use textures.
         if (TileOnlyNeedsPartialUpdate(tile) &&
             layer_tree_host()->RequestPartialTextureUpdate()) {
           tile->partial_update = true;
         } else {
           tile->dirty_rect = tiler_->TileRect(tile);
@@ skipping 437 matching lines @@
   gfx::Rect prepaint_rect = visible_content_rect();
   prepaint_rect.Inset(-tiler_->tile_size().width() * kPrepaintColumns,
                       -tiler_->tile_size().height() * kPrepaintRows);
   gfx::Rect content_rect(content_bounds());
   prepaint_rect.Intersect(content_rect);
 
   return prepaint_rect;
 }
 
 }  // namespace cc