Adding fromRect to DOMRect and DOMRectReadOnly interfaces following spec.

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

Index: third_party/WebKit/Source/core/dom/DOMRectReadOnly.cpp
diff --git a/third_party/WebKit/Source/core/dom/DOMRectReadOnly.cpp b/third_party/WebKit/Source/core/dom/DOMRectReadOnly.cpp
index 3b09920df6ed806de5715b72aeff6ee9a89f1750..6b6e5154c45cc9fcfd9cddba2b5ff6c5ec36828c 100644
--- a/third_party/WebKit/Source/core/dom/DOMRectReadOnly.cpp
+++ b/third_party/WebKit/Source/core/dom/DOMRectReadOnly.cpp
@@ -6,6 +6,7 @@
 
 #include "bindings/core/v8/ScriptValue.h"
 #include "bindings/core/v8/V8ObjectBuilder.h"
+#include "core/dom/DOMRectInit.h"
 
 namespace blink {
 
@@ -29,6 +30,10 @@ ScriptValue DOMRectReadOnly::toJSONForBinding(ScriptState* scriptState) const {
   return result.scriptValue();
 }
 
+DOMRectReadOnly* DOMRectReadOnly::fromRect(const DOMRectInit& other) {
+  return new DOMRectReadOnly(other.x(), other.y(), other.width(), other.height());
+}
+
 DOMRectReadOnly::DOMRectReadOnly(double x,
                                  double y,
                                  double width,