cc: Allow output readback/copy requests to specify a sub-rect to copy.

cc/output/gl_renderer.cc

 // Copyright 2010 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/output/gl_renderer.h"
 
 #include <algorithm>
 #include <limits>
 #include <set>
 #include <string>
@@ skipping 1896 matching lines @@
     return;
 
   FlushTextureQuadCache();
   GLC(context_, context_->disable(GL_SCISSOR_TEST));
   is_scissor_enabled_ = false;
 }
 
 void GLRenderer::CopyCurrentRenderPassToBitmap(
     DrawingFrame* frame,
     scoped_ptr<CopyOutputRequest> request) {
-  GetFramebufferPixelsAsync(frame->current_render_pass->output_rect,
-                            request.Pass());
+  gfx::Rect copy_rect = frame->current_render_pass->output_rect;
+  if (request->has_area()) {
+    // Intersect with the request's area, positioned with its origin at the
+    // origin of the full copy_rect.
+    copy_rect.Intersect(request->area() - copy_rect.OffsetFromOrigin());
+  }
+  GetFramebufferPixelsAsync(copy_rect, request.Pass());
 }
 
 void GLRenderer::ToGLMatrix(float* gl_matrix, const gfx::Transform& transform) {
   transform.matrix().asColMajorf(gl_matrix);
 }
 
 void GLRenderer::SetShaderQuadF(const gfx::QuadF& quad, int quad_location) {
   if (quad_location == -1)
     return;
 
@@ skipping 1100 matching lines @@
   // The Skia GPU backend requires a stencil buffer.  See ReinitializeGrCanvas
   // implementation.
   return gr_context_ && context_->getContextAttributes().stencil;
 }
 
 bool GLRenderer::IsContextLost() {
   return (context_->getGraphicsResetStatusARB() != GL_NO_ERROR);
 }
 
 }  // namespace cc