Always composite position: fixed elements with composited descendants.

third_party/WebKit/Source/platform/graphics/CompositingReasons.cpp

 // Copyright 2014 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 "platform/graphics/CompositingReasons.h"
 
 #include "wtf/StdLibExtras.h"
 
 namespace blink {
@@ skipping 127 matching lines @@
         "Has a perspective transform that needs to be known by compositor because of 3d descendants" },
     { CompositingReasonPreserve3DWith3DDescendants,
         "preserve3DWith3DDescendants",
         "Has a preserves-3d property that needs to be known by compositor because of 3d descendants" },
     { CompositingReasonReflectionOfCompositedParent,
         "reflectionOfCompositedParent",
         "Is a reflection of a composited layer" },
     { CompositingReasonIsolateCompositedDescendants,
         "isolateCompositedDescendants",
         "Should isolate descendants to apply a blend effect" },
+    { CompositingReasonPositionFixedWithCompositedDescendants,
+        "positionFixedWithCompositedDescendants"
+        "Is a position:fixed element with composited descendants" },
     { CompositingReasonRoot,
         "root",
         "Is the root layer" },
     { CompositingReasonLayerForAncestorClip,
         "layerForAncestorClip",
         "Secondary layer, applies a clip due to a sibling in the compositing tree" },
     { CompositingReasonLayerForDescendantClip,
         "layerForDescendantClip",
         "Secondary layer, to clip descendants of the owning layer" },
     { CompositingReasonLayerForPerspective,
@@ skipping 39 matching lines @@
         "layerForScrollingBlockSelection",
         "Secondary layer, to house block selection gaps for composited scrolling with no scrolling contents" },
     { CompositingReasonInlineTransform,
         "inlineTransform",
         "Has an inline transform, which causes subsequent layers to assume overlap" },
 };
 
 size_t kNumberOfCompositingReasons = WTF_ARRAY_LENGTH(kCompositingReasonStringMap);
 
 } // namespace blink