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..8af1ed32e423771b37ec75cbb1a7ad4479f86f9b 100644
--- a/third_party/WebKit/Source/core/layout/svg/LayoutSVGContainer.h
+++ b/third_party/WebKit/Source/core/layout/svg/LayoutSVGContainer.h
@@ -70,8 +70,17 @@ protected:
 
     bool nodeAtFloatPoint(HitTestResult&, const FloatPoint& pointInParent, HitTestAction) override;
 
+    // The following enumeration is used to optimize cases where the scale is
+    // known to be invariant (see: LayoutSVGContainer::layout). The value
+    // 'Full' can be used in the general case when the scale change is unknown,
+    // or known to change.
+    enum class TransformChange {
+        None,
+        ScaleInvariant,
+        Full,
+    };
     // Allow LayoutSVGTransformableContainer to hook in at the right time in layout().
-    virtual bool calculateLocalTransform() { return false; }
+    virtual TransformChange calculateLocalTransform() { return TransformChange::None; }
 
     // Allow LayoutSVGViewportContainer to hook in at the right times in layout() and nodeAtFloatPoint().
     virtual void calcViewport() { }