Don't shrink starting_rect in the first round.

cc/resources/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/resources/picture_layer_tiling.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/debug/trace_event.h"
@@ skipping 512 matching lines @@
   if (starting_rect.IsEmpty())
     return starting_rect;
 
   DCHECK(!bounding_rect.IsEmpty());
   DCHECK_GT(target_area, 0);
 
   // Expand the starting rect to cover target_area.
   int delta = ComputeExpansionDelta(
       2, 2, starting_rect.width(), starting_rect.height(), target_area);
   gfx::Rect expanded_starting_rect = starting_rect;
-  expanded_starting_rect.Inset(-delta, -delta);
+
+  // Expand but not shink the starting_rect to include small layers that are
+  // in viewport but target_area is smaller than the viewport.
+  if (delta > 0)
+    expanded_starting_rect.Inset(-delta, -delta);
 
   gfx::Rect rect = IntersectRects(expanded_starting_rect, bounding_rect);
   if (rect.IsEmpty()) {
     // The starting_rect and bounding_rect are far away.
     return rect;
   }
-  if (rect == expanded_starting_rect) {
+  if (delta >= 0 && rect == expanded_starting_rect) {
     // The expanded starting rect already covers target_area on bounding_rect.
     return rect;
   }
 
   // Continue to expand rect to let it cover target_area.
 
   // These values will be updated by the loop and uses as the output.
   int origin_x = rect.x();
   int origin_y = rect.y();
   int width = rect.width();
@@ skipping 61 matching lines @@
 
     // If our delta is less then our event distance, we're done.
     if (delta < event.distance)
       break;
   }
 
   return gfx::Rect(origin_x, origin_y, width, height);
 }
 
 }  // namespace cc