[Fixed Position] Add image proxy

Add selection proxy for image elements to support image URL
dialog, WTD-881.

platform/features/layout/test/elements/ImageProxySpec.js

@@ -0,0 +1,37 @@
+/*global define,describe,it,expect,beforeEach,jasmine*/
+
+define(
+    ['../../src/elements/ImageProxy'],
+    function (ImageProxy) {
+        "use strict";
+
+        describe("A fixed position image proxy", function () {
+            var testElement,
+                testElements,
+                proxy;
+
+            beforeEach(function () {
+                testElement = {
+                    x: 1,
+                    y: 2,
+                    width: 42,
+                    height: 24,
+                    url: "http://www.nasa.gov"
+                };
+                testElements = [ {}, {}, testElement, {} ];
+                proxy = new ImageProxy(
+                    testElement,
+                    testElements.indexOf(testElement),
+                    testElements
+                );
+            });
+
+            it("provides getter/setter for image URL", function () {
+                expect(proxy.url()).toEqual("http://www.nasa.gov");
+                expect(proxy.url("http://www.nasa.gov/some.jpg"))
+                    .toEqual("http://www.nasa.gov/some.jpg");
+                expect(proxy.url()).toEqual("http://www.nasa.gov/some.jpg");
+            });
+        });
+    }
+);