cc: Async readback.

cc/output/gl_renderer.cc

Index: cc/output/gl_renderer.cc
diff --git a/cc/output/gl_renderer.cc b/cc/output/gl_renderer.cc
index 19b215b76dc0d4cc90edabc6a35dc36537cdb29c..4a0c7ba1fcf3d132ce09bcb04e7b269e748b19bc 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -1776,6 +1776,19 @@ void GLRenderer::EnsureScissorTestDisabled() {
   is_scissor_enabled_ = false;
 }
 
+void GLRenderer::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());
+  if (bitmap->allocPixels()) {
+    bitmap->lockPixels();
+    GetFramebufferPixels(bitmap->getPixels(), gfx::Rect(render_pass_size));
+    bitmap->unlockPixels();
+  }
+}
+
 void GLRenderer::ToGLMatrix(float* gl_matrix, const gfx::Transform& transform) {
   transform.matrix().asColMajorf(gl_matrix);
 }