Make CaretBase a DisplayItemClient.

third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.h

Index: third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.h
diff --git a/third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.h b/third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.h
index 08b05b896198fc4b4da5341a6afd35eb687b8acd..1ad695bd8e715b48d26fcbf9ef1718121aaf6d07 100644
--- a/third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.h
+++ b/third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.h
@@ -51,7 +51,8 @@ public:
 
     // Invalidate the paint of a specific subrectangle within a given object. The rect is in the object's coordinate space.
     // If a DisplayItemClient is specified, that client is invalidated rather than |m_object|.
-    void invalidatePaintRectangle(const LayoutRect&, DisplayItemClient*);
+    // Returns the visual rect that was invalidated (i.e, invalidation in the space of the GraphicsLayer backing this LayoutObject).
+    LayoutRect invalidatePaintRectangle(const LayoutRect&, DisplayItemClient*);
 
     void invalidatePaintIncludingNonCompositingDescendants();
     void invalidatePaintIncludingNonSelfPaintingLayerDescendants(const LayoutBoxModelObject& paintInvalidationContainer);