Increase width of viewportConstrainedNotCompositingReasons

Source/core/rendering/RenderLayer.h

Index: Source/core/rendering/RenderLayer.h
diff --git a/Source/core/rendering/RenderLayer.h b/Source/core/rendering/RenderLayer.h
index b0e5ffbd6c6cbd34717db55785cace48550097dc..17489c623e83a2beed749f88439f215b3d452f8d 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -423,6 +423,8 @@ public:
     bool isInTopLayer() const;
     bool isInTopLayerSubtree() const;
 
+    // Note: this is internally stored using a minimal number of bits. Ensure
+    // that you have enough when you add to this enum!
     enum ViewportConstrainedNotCompositedReason {
         NoNotCompositedReason,
         NotCompositedForBoundsOutOfView,
@@ -431,7 +433,14 @@ public:
         NotCompositedForUnscrollableAncestors,
     };
 
-    void setViewportConstrainedNotCompositedReason(ViewportConstrainedNotCompositedReason reason) { m_compositingProperties.viewportConstrainedNotCompositedReason = reason; }
+    void setViewportConstrainedNotCompositedReason(ViewportConstrainedNotCompositedReason reason)
+    {
+        m_compositingProperties.viewportConstrainedNotCompositedReason = reason;
+        // This can fail if we forget to change the width of the viewportConstrainedNotCompositedReason
+        // when we update the enum.
+        ASSERT(viewportConstrainedNotCompositedReason() == reason);

[enne (OOO), 2014/02/28 20:28:46]

Compile assert?

+    }
+
     ViewportConstrainedNotCompositedReason viewportConstrainedNotCompositedReason() const { return static_cast<ViewportConstrainedNotCompositedReason>(m_compositingProperties.viewportConstrainedNotCompositedReason); }
 
     bool isOutOfFlowRenderFlowThread() const { return renderer()->isOutOfFlowRenderFlowThread(); }
@@ -731,7 +740,7 @@ protected:
         bool lostGroupedMapping : 1;
 
         // The reason, if any exists, that a fixed-position layer is chosen not to be composited.
-        unsigned viewportConstrainedNotCompositedReason : 2;
+        unsigned viewportConstrainedNotCompositedReason : 3;
 
         // Once computed, indicates all that a layer needs to become composited using the CompositingReasons enum bitfield.
         CompositingReasons compositingReasons;