Support browser side thumbnailing for GPU composited pages on Windows.

content/browser/renderer_host/render_widget_host_win.cc

+// Copyright (c) 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 "content/browser/renderer_host/render_widget_host.h"
+
+#include "base/win/scoped_hdc.h"
+#include "content/public/browser/render_widget_host_view.h"
+#include "skia/ext/platform_canvas.h"
+#include "ui/gfx/rect.h"
+
+bool RenderWidgetHostImpl::CopyFromCompositingSurface(
+    skia::PlatformCanvas* output) {
+  if (!is_accelerated_compositing_active_)
+    return false;
+
+  if (!view())
+    return false;
+
+  const gfx::Rect bounds = view()->GetViewBounds();
+  if (!output->initialize(bounds.width(), bounds.height(), true))
+    return false;
+
+  skia::ScopedPlatformPaint scoped_platform_paint(output);
+  gfx::NativeWindow window_handle = GetCompositingSurface().handle;
+  base::win::ScopedGetDC window_hdc(window_handle);
+  HDC temp_dc = scoped_platform_paint.GetPlatformSurface();
+  return BitBlt(temp_dc, 0, 0, bounds.width(), bounds.height(), window_hdc,

[vangelis, 2012/03/05 06:20:55]

I think ideally we'll want to get the bits out of the compositing surfaces'
accelerated_surface here.  I'm also worried about possible race conditions as
calling GetPlatformSurface() will actually even create a window if one doesn't
yet exist so there are not guarantees that we'll get fresh output here.

[mazda, 2012/03/05 15:54:14]

Did you mean GetCompositingSurface()?
I plan to move these code to RenderWidgetHostViewWin as brettw suggested, where
we can check the existence of |compositor_host_window_|.

+                0, 0, SRCCOPY) != 0;
+}