Dirty rects always contain full tiles with delegated rendering.

cc/resources/bitmap_content_layer_updater.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/resources/bitmap_content_layer_updater.h"
 
 #include "cc/debug/devtools_instrumentation.h"
 #include "cc/debug/rendering_stats_instrumentation.h"
 #include "cc/resources/layer_painter.h"
 #include "cc/resources/prioritized_resource.h"
@@ skipping 37 matching lines @@
 BitmapContentLayerUpdater::~BitmapContentLayerUpdater() {}
 
 scoped_ptr<LayerUpdater::Resource> BitmapContentLayerUpdater::CreateResource(
     PrioritizedResourceManager* manager) {
   return scoped_ptr<LayerUpdater::Resource>(
       new Resource(this, PrioritizedResource::Create(manager)));
 }
 
 void BitmapContentLayerUpdater::PrepareToUpdate(
     gfx::Rect content_rect,
+    gfx::Rect paint_rect,
     gfx::Size tile_size,
     float contents_width_scale,
     float contents_height_scale,
     gfx::Rect* resulting_opaque_rect) {
   devtools_instrumentation::ScopedLayerTask paint_layer(
       devtools_instrumentation::kPaintLayer, layer_id_);
   if (canvas_size_.width() < content_rect.size().width() ||
       canvas_size_.height() < content_rect.size().height()) {
     devtools_instrumentation::ScopedLayerTask paint_setup(
         devtools_instrumentation::kPaintSetup, layer_id_);
     canvas_size_ = content_rect.size();
     bitmap_backing_.setConfig(
         SkBitmap::kARGB_8888_Config,
         canvas_size_.width(), canvas_size_.height(),
         0, layer_is_opaque_ ? kOpaque_SkAlphaType : kPremul_SkAlphaType);
     bitmap_backing_.allocPixels();
     canvas_ = skia::AdoptRef(new SkCanvas(bitmap_backing_));
   }
 
   base::TimeTicks start_time =
       rendering_stats_instrumentation_->StartRecording();
   PaintContents(canvas_.get(),
                 content_rect,
+                paint_rect,
                 contents_width_scale,
                 contents_height_scale,
                 resulting_opaque_rect);
   base::TimeDelta duration =
       rendering_stats_instrumentation_->EndRecording(start_time);
   rendering_stats_instrumentation_->AddPaint(
       duration,
       content_rect.width() * content_rect.height());
 }
 
 void BitmapContentLayerUpdater::UpdateTexture(ResourceUpdateQueue* queue,
                                               PrioritizedResource* texture,
                                               gfx::Rect source_rect,
                                               gfx::Vector2d dest_offset,
                                               bool partial_update) {
   CHECK(canvas_);
-  gfx::Rect canvas_rect = content_rect();
+  gfx::Rect canvas_rect = paint_rect();
   canvas_rect.set_size(canvas_size_);
   ResourceUpdate upload = ResourceUpdate::CreateFromCanvas(
       texture, canvas_, canvas_rect, source_rect, dest_offset);
   if (partial_update)
     queue->AppendPartialUpload(upload);
   else
     queue->AppendFullUpload(upload);
 }
 
 void BitmapContentLayerUpdater::ReduceMemoryUsage() {
   canvas_.clear();
   canvas_size_ = gfx::Size();
 }
 
 void BitmapContentLayerUpdater::SetOpaque(bool opaque) {
   if (opaque != layer_is_opaque_) {
     canvas_.clear();
     canvas_size_ = gfx::Size();
   }
 
   ContentLayerUpdater::SetOpaque(opaque);
 }
 
 }  // namespace cc