v8binding: Implements an alternative of WindowProxy.[[DefineOwnProperty]].

third_party/WebKit/Source/core/frame/DOMWindow.cpp

Index: third_party/WebKit/Source/core/frame/DOMWindow.cpp
diff --git a/third_party/WebKit/Source/core/frame/DOMWindow.cpp b/third_party/WebKit/Source/core/frame/DOMWindow.cpp
index fa9d7601038597b8aaacb573e1d15af92a3308b4..311259e0d8ceed702c94615e060d26e66876b196 100644
--- a/third_party/WebKit/Source/core/frame/DOMWindow.cpp
+++ b/third_party/WebKit/Source/core/frame/DOMWindow.cpp
@@ -115,6 +115,18 @@ DOMWindow* DOMWindow::AnonymousIndexedGetter(uint32_t index) const {
   return child ? child->DomWindow() : nullptr;
 }
 
+bool DOMWindow::AnonymousIndexedSetter(uint32_t index,
+                                       const ScriptValue& value) {
+  // https://html.spec.whatwg.org/C/browsers.html#windowproxy-defineownproperty
+  //   step 2 - 1. If P is an array index property name, return false.
+  //
+  // As an alternative way to implement WindowProxy.[[DefineOwnProperty]] for
+  // array index property names, we always intercept and ignore the set
+  // operation for indexed properties, i.e. [[DefineOwnProperty]] for array
+  // index property names has always no effect.
+  return true;  // Intercept unconditionally but do nothing.
+}
+
 bool DOMWindow::IsCurrentlyDisplayedInFrame() const {
   if (GetFrame())
     SECURITY_CHECK(GetFrame()->DomWindow() == this);