Generate fewer tiles when zooming in.

cc/picture_layer_tiling.cc

 // Copyright 2012 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/picture_layer_tiling.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/math_util.h"
 #include "ui/gfx/point_conversions.h"
 #include "ui/gfx/rect_conversions.h"
@@ skipping 355 matching lines @@
       last_layer_bounds == current_layer_bounds &&
       last_layer_content_bounds == current_layer_content_bounds &&
       last_layer_contents_scale == current_layer_contents_scale) {
     time_delta = current_frame_time - last_impl_frame_time_;
   }
 
   gfx::Rect viewport_in_content_space =
       gfx::ToEnclosingRect(gfx::ScaleRect(viewport_in_layer_space,
                                           contents_scale_));
   gfx::Rect inflated_rect = viewport_in_content_space;
+  float adjusted_inset = TilePriority::kMaxDistanceInContentSpace /
+                         std::max(contents_scale_, 1.f);
   inflated_rect.Inset(
-      -TilePriority::kMaxDistanceInContentSpace,
-      -TilePriority::kMaxDistanceInContentSpace,
-      -TilePriority::kMaxDistanceInContentSpace,
-      -TilePriority::kMaxDistanceInContentSpace);
+      -adjusted_inset,
+      -adjusted_inset,
+      -adjusted_inset,
+      -adjusted_inset);
   inflated_rect.Intersect(ContentRect());
 
   // Iterate through all of the tiles that were live last frame but will
   // not be live this frame, and mark them as being dead.
   for (TilingData::DifferenceIterator iter(&tiling_data_,
                                            last_prioritized_rect_,
                                            inflated_rect);
        iter;
        ++iter) {
     TileMap::iterator find = tiles_.find(iter.index());
@@ skipping 105 matching lines @@
     // and recreated, then that picture pile ref could exist indefinitely.  To
     // prevent this, ask the client to update the pile to its own ref.  This
     // will cause PicturePileImpls and their clones to get deleted once the
     // corresponding PictureLayerImpl and any in flight raster jobs go out of
     // scope.
     client_->UpdatePile(it->second);
   }
 }
 
 }  // namespace cc