Reland: Don't early out recursion into PaintLayerChildren when computing composited bounds.

third_party/WebKit/Source/core/paint/PaintLayerClipperTest.cpp

 // Copyright 2016 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 "core/paint/PaintLayerClipper.h"
 
 #include "core/layout/LayoutBoxModelObject.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/PaintLayer.h"
@@ skipping 98 matching lines @@
   EXPECT_EQ(LayoutRect(0, 0, 200, 400), layerBounds);
 
   ClipRectsContext contextClip(layer->parent(), PaintingClipRects);
   layer->clipper().calculateRects(contextClip, infiniteRect, layerBounds,
                                   backgroundRect, foregroundRect);
   EXPECT_EQ(LayoutRect(0, 0, 200, 200), backgroundRect.rect());
   EXPECT_EQ(LayoutRect(0, 0, 200, 200), foregroundRect.rect());
   EXPECT_EQ(LayoutRect(0, 0, 200, 400), layerBounds);
 }
 
+TEST_F(PaintLayerClipperTest, LocalClipRectFixedUnderTransform) {
+  setBodyInnerHTML(
+      "<div id='transformed'"
+      "    style='will-change: transform; width: 100px; height: 100px;"
+      "    overflow: hidden'>"
+      "  <div id='fixed' "
+      "      style='position: fixed; width: 100px; height: 100px;"
+      "      top: -50px'>"
+      "   </div>"
+      "</div>");
+
+  LayoutRect infiniteRect(LayoutRect::infiniteIntRect());
+  PaintLayer* transformed =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("transformed"))
+          ->layer();
+  PaintLayer* fixed =
+      toLayoutBoxModelObject(getLayoutObjectByElementId("fixed"))->layer();
+
+  EXPECT_EQ(LayoutRect(0, 0, 100, 100),
+            transformed->clipper().localClipRect(transformed));
+  EXPECT_EQ(LayoutRect(0, 50, 100, 100),
+            fixed->clipper().localClipRect(transformed));
+}
+
 }  // namespace blink