Limit size of scaled layer rects in ScrollbarLayer to content_bounds().

cc/layers/scrollbar_layer.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/layers/scrollbar_layer.h"
 
 #include "base/auto_reset.h"
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
 #include "cc/layers/scrollbar_layer_impl.h"
@@ skipping 340 matching lines @@
     resource->texture()->ReturnBackingTexture();
 
   gfx::Vector2d dest_offset(0, 0);
   resource->Update(queue, rect, dest_offset, partial_updates_allowed, stats);
 }
 
 gfx::Rect ScrollbarLayer::ScrollbarLayerRectToContentRect(
     gfx::Rect layer_rect) const {
   // Don't intersect with the bounds as in LayerRectToContentRect() because
   // layer_rect here might be in coordinates of the containing layer.
-  return gfx::ScaleToEnclosingRect(layer_rect,
-                                   contents_scale_y(),
-                                   contents_scale_y());
+  gfx::Rect expanded_rect = gfx::ScaleToEnclosingRect(
+      layer_rect, contents_scale_y(), contents_scale_y());
+  // We should never return a rect bigger than the content_bounds().
+  gfx::Size clamped_size = expanded_rect.size();
+  clamped_size.ClampToMax(content_bounds());
+  expanded_rect.set_size(clamped_size);
+  return expanded_rect;
 }
 
 void ScrollbarLayer::SetTexturePriorities(
     const PriorityCalculator& priority_calc) {
   if (layer_tree_host()->settings().solid_color_scrollbars)
     return;
 
   if (content_bounds().IsEmpty())
     return;
   DCHECK_LE(content_bounds().width(), MaxTextureSize());
@@ skipping 64 matching lines @@
                thumb_.get(),
                origin_thumb_rect,
                queue,
                stats);
   }
 
   dirty_rect_ = gfx::RectF();
 }
 
 }  // namespace cc