Add a FOUC painting test.

Source/web/tests/sim/SimDisplayItemList.cpp

+// Copyright 2015 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 "config.h"
+#include "web/tests/sim/SimDisplayItemList.h"
+
+#include "third_party/skia/include/core/SkPicture.h"
+
+namespace blink {
+
+SimDisplayItemList::SimDisplayItemList()
+    : m_didDrawText(false)
+    , m_drawCount(0)
+{
+}
+
+void SimDisplayItemList::appendDrawingItem(const SkPicture* picture)
+{
+    // There's not much we can tell about a picture, but we can tell if it

[jbroman, 2015/09/06 17:00:51]

It's possible to play a picture back to a mock SkCanvas to figure out what was
drawn.

[esprehn, 2015/09/06 20:27:58]

Using gtest mocks? The SkCanvas isn't virtual. Do you have an example?

[esprehn, 2015/09/06 21:17:56]

Oh I see all the onDraw* virtual methods that the non virtual ones call. I'll
look into that for future tests. Thanks!

[jbroman, 2015/09/07 00:52:37]

Yeah. Here's a simple example of this in a test (the Slimming Paint path uses
SkPicture::playback with the mock canvas).
https://chromium.googlesource.com/chromium/blink/+/98a45304/Source/web/PageOv...

+    // contains text. Ideally paint slimming would have a higher level
+    // display list (or special GraphicsContext) so unit tests could query
+    // what kind of things were painted.
+    m_didDrawText |= picture->hasText();
+    m_drawCount += picture->approximateOpCount();
+}
+
+} // namespace blink