Avoid using forced layout to trigger paint invalidation for SVG containers

third_party/WebKit/Source/core/layout/svg/LayoutSVGContainer.h

Index: third_party/WebKit/Source/core/layout/svg/LayoutSVGContainer.h
diff --git a/third_party/WebKit/Source/core/layout/svg/LayoutSVGContainer.h b/third_party/WebKit/Source/core/layout/svg/LayoutSVGContainer.h
index b3e1fee76f54b0702a8245d1e07258392ff4c978..59165baf84ee12b2484b8b07835036cf1147874e 100644
--- a/third_party/WebKit/Source/core/layout/svg/LayoutSVGContainer.h
+++ b/third_party/WebKit/Source/core/layout/svg/LayoutSVGContainer.h
@@ -70,8 +70,13 @@ protected:
 
     bool nodeAtFloatPoint(HitTestResult&, const FloatPoint& pointInParent, HitTestAction) override;
 
+    enum TransformChangeFlags {

[pdr., 2016/06/15 12:15:17]

Returning just ScaleChange from LayoutSVGResourceMarker::calculateLocalTransform
might introduce bugs because the TransformChange bit will be 0.

WDYT about switching the logic and renaming ScaleChange to
ScaleKnownToBeUnchanged?

[fs, 2016/06/15 22:10:33]

Yes, not too happy about this bit (no pun intended). Returning a "negative" bit
might work for now. 

[fs, 2016/06/20 11:48:49]

Rewrote it to use an (ordered) enumeration instead. Maybe a little better, WDYT?
PTAL.

+        NoTransformChange = 0,
+        TransformChange = 1u << 0,
+        ScaleChange = 1u << 1,
+    };
     // Allow LayoutSVGTransformableContainer to hook in at the right time in layout().
-    virtual bool calculateLocalTransform() { return false; }
+    virtual unsigned calculateLocalTransform() { return NoTransformChange; }
 
     // Allow LayoutSVGViewportContainer to hook in at the right times in layout() and nodeAtFloatPoint().
     virtual void calcViewport() { }