[Fixed Position] Add unit tests for new code

Refactored ElementProxy and UnitAccessorMutator slightly to improve encasulation. Added unit tests for UnitAccessorMutator

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

@@ -0,0 +1,72 @@
+define(
+    ['../../src/elements/UnitAccessorMutator'],
+    function (UnitAccessorMutator) {
+
+        var GRID_SIZE = [13,17];
+
+        describe("An elementProxy.gridSize accessor-mutator", function () {
+            var mockElementProxy,
+                testElement,
+                uAM;
+
+            beforeEach(function () {
+                testElement = {
+                    x: 2,
+                    y: 3,
+                    width: 4,
+                    height: 5,
+                    useGrid: true
+                };
+
+                mockElementProxy = {
+                    element: testElement,
+                    gridSize: GRID_SIZE,
+                    getMinHeight: jasmine.createSpy('minHeight'),
+                    getMinWidth: jasmine.createSpy('minWidth')
+                };
+
+                uAM = new UnitAccessorMutator(mockElementProxy);
+
+                mockElementProxy.getMinWidth.andReturn(1);
+                mockElementProxy.getMinHeight.andReturn(1);
+
+            });
+
+            it("allows access to useGrid", function () {
+                expect(uAM()).toEqual(mockElementProxy.element.useGrid);
+            });
+
+            it("allows mutation of useGrid", function () {
+                uAM(false);
+                expect(mockElementProxy.element.useGrid).toEqual(false);
+            });
+
+            it("converts coordinates appropriately", function () {
+                uAM(false);
+                expect(mockElementProxy.element.x).toEqual(26);
+                expect(mockElementProxy.element.y).toEqual(51);
+                expect(mockElementProxy.element.width).toEqual(52);
+                expect(mockElementProxy.element.height).toEqual(85);
+                uAM(true);
+                expect(mockElementProxy.element.x).toEqual(2);
+                expect(mockElementProxy.element.y).toEqual(3);
+                expect(mockElementProxy.element.width).toEqual(4);
+                expect(mockElementProxy.element.height).toEqual(5);
+            });
+
+            it("doesn't covert coordinates unecessarily", function () {
+                uAM(false);
+                expect(mockElementProxy.element.x).toEqual(26);
+                expect(mockElementProxy.element.y).toEqual(51);
+                expect(mockElementProxy.element.width).toEqual(52);
+                expect(mockElementProxy.element.height).toEqual(85);
+                uAM(false);
+                expect(mockElementProxy.element.x).toEqual(26);
+                expect(mockElementProxy.element.y).toEqual(51);
+                expect(mockElementProxy.element.width).toEqual(52);
+                expect(mockElementProxy.element.height).toEqual(85);
+            });
+
+        });
+    }
+);