cc: Async readback.

cc/output/software_renderer.cc

Index: cc/output/software_renderer.cc
diff --git a/cc/output/software_renderer.cc b/cc/output/software_renderer.cc
index fec4f3e184c8aca11023fbc1dc8218b5f9369f61..69c3b7e8bb50ec8e869c6d0b51a388cb5fd7d679 100644
--- a/cc/output/software_renderer.cc
+++ b/cc/output/software_renderer.cc
@@ -407,6 +407,15 @@ void SoftwareRenderer::DrawUnsupportedQuad(const DrawingFrame* frame,
                             current_paint_);
 }
 
+void SoftwareRenderer::CopyCurrentRenderPassToBitmap(DrawingFrame* frame,
+                                                     SkBitmap* bitmap) {
+  gfx::Size render_pass_size = frame->current_render_pass->output_rect.size();
+  bitmap->setConfig(SkBitmap::kARGB_8888_Config,
+                    render_pass_size.width(),
+                    render_pass_size.height());
+  current_canvas_->readPixels(bitmap, 0, 0);
+}
+
 void SoftwareRenderer::GetFramebufferPixels(void* pixels, gfx::Rect rect) {
   TRACE_EVENT0("cc", "SoftwareRenderer::GetFramebufferPixels");
   SkBitmap subset_bitmap;