Make CaretBase a DisplayItemClient.

third_party/WebKit/Source/core/layout/LayoutObject.h

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index c80c9bb0d936bf93b20f0aa2fe4136868db93ae6..a2816297526db24266be19aff26e2af74e2d2f99 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -1108,7 +1108,8 @@ 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 |this|.
-    void invalidatePaintRectangle(const LayoutRect&, DisplayItemClient* = nullptr) const;
+    // Returns the visual rect that was invalidated (i.e, invalidation in the space of the GraphicsLayer backing this LayoutObject).
+    LayoutRect invalidatePaintRectangle(const LayoutRect&, DisplayItemClient* = nullptr) const;
 
     // Walk the tree after layout issuing paint invalidations for layoutObjects that have changed or moved, updating bounds that have changed, and clearing paint invalidation state.
     virtual void invalidateTreeIfNeeded(const PaintInvalidationState&);