The DOMRectReadOnly implementation are different with spec.

third_party/WebKit/Source/core/dom/DOMRectReadOnly.idl

Index: third_party/WebKit/Source/core/dom/DOMRectReadOnly.idl
diff --git a/third_party/WebKit/Source/core/dom/DOMRectReadOnly.idl b/third_party/WebKit/Source/core/dom/DOMRectReadOnly.idl
index 2f1c37f99f0cf4406f4585ac5545c8604c337867..045afd3ad9ecb920961828e99bdfcef9232c6956 100644
--- a/third_party/WebKit/Source/core/dom/DOMRectReadOnly.idl
+++ b/third_party/WebKit/Source/core/dom/DOMRectReadOnly.idl
@@ -5,8 +5,8 @@
 // https://dev.w3.org/fxtf/geometry/#DOMRect
 
 [
-    Constructor(unrestricted double x, unrestricted double y,
-                unrestricted double width, unrestricted double height),
+    Constructor(optional unrestricted double x = 0, optional unrestricted double y = 0,
+                optional unrestricted double width = 0, optional unrestricted double height = 0),
     // FIXME: Exposed=(Window,Worker)
     RuntimeEnabled=GeometryInterfaces,
 ] interface DOMRectReadOnly {