Generate fewer tiles when zooming in.

cc/picture_layer_tiling.cc

Index: cc/picture_layer_tiling.cc
diff --git a/cc/picture_layer_tiling.cc b/cc/picture_layer_tiling.cc
index 214bcd37f7a14a5f3becc3085361713f636b2187..ae3afc39d0451f79f96449138fba168f8f90ae2a 100644
--- a/cc/picture_layer_tiling.cc
+++ b/cc/picture_layer_tiling.cc
@@ -373,11 +373,13 @@ void PictureLayerTiling::UpdateTilePriorities(
       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