Move make_dart_rectangle to html_common

sdk/lib/html/html_common/conversions_dartium.dart

Index: sdk/lib/html/html_common/conversions_dartium.dart
diff --git a/sdk/lib/html/html_common/conversions_dartium.dart b/sdk/lib/html/html_common/conversions_dartium.dart
index d6e606464dfd496221be385328adc28b35ebaad1..28225f089f67d3c50b89df6cf00a9db5a88c8778 100644
--- a/sdk/lib/html/html_common/conversions_dartium.dart
+++ b/sdk/lib/html/html_common/conversions_dartium.dart
@@ -66,3 +66,12 @@ Future convertNativePromiseToDartFuture(js.JsObject promise) {
 convertDartToNative_DateTime(DateTime date) {
   return new js.JsObject(js.context["Date"], [date.millisecondsSinceEpoch]);
 }
+
+/// Creates a Dart Rectangle from a Javascript object with properties
+/// left, top, width and height. Used internally in Dartium.
+Rectangle make_dart_rectangle(r) =>
+    r == null ? null : new Rectangle(
+    js.JsNative.getProperty(r, 'left'),
+    js.JsNative.getProperty(r, 'top'),
+    js.JsNative.getProperty(r, 'width'),
+    js.JsNative.getProperty(r, 'height'));