Adding fromRect to DOMRect and DOMRectReadOnly interfaces following spec.

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

Index: third_party/WebKit/Source/core/dom/DOMRect.cpp
diff --git a/third_party/WebKit/Source/core/dom/DOMRect.cpp b/third_party/WebKit/Source/core/dom/DOMRect.cpp
index 26c811aed41d2c561861f176e5039465649bbe70..002018ab19887b31b3cf277af3d5c2b919c472d5 100644
--- a/third_party/WebKit/Source/core/dom/DOMRect.cpp
+++ b/third_party/WebKit/Source/core/dom/DOMRect.cpp
@@ -4,12 +4,18 @@
 
 #include "core/dom/DOMRect.h"
 
+#include "core/dom/DOMRectInit.h"
+
 namespace blink {
 
 DOMRect* DOMRect::create(double x, double y, double width, double height) {
   return new DOMRect(x, y, width, height);
 }
 
+DOMRect* DOMRect::fromRect(const DOMRectInit& other) {
+  return new DOMRect(other.x(), other.y(), other.width(), other.height());
+}
+
 DOMRect::DOMRect(double x, double y, double width, double height)
     : DOMRectReadOnly(x, y, width, height) {}