Removing webkit-prefixed image data HD APIs from 2D canvas

LayoutTests/fast/canvas/2d.backingStorePixelRatio.html

-<pre id="console"></pre>
-<script>
-    function log(message)
-    {
-        document.getElementById("console").appendChild(document.createTextNode(message + "\n"));
-    }
-
-    if (window.testRunner) {
-        testRunner.dumpAsText();
-        var canvas1 = document.createElement("canvas");
-        var context1 = canvas1.getContext("2d");
-
-        testRunner.waitUntilDone();
-        testRunner.setBackingScaleFactor(2, function() {
-            var canvas2 = document.createElement("canvas");
-            var context2 = canvas2.getContext("2d");
-
-            log ("context1.webkitBackingStorePixelRatio is " + context1.webkitBackingStorePixelRatio);
-            log ("context2.webkitBackingStorePixelRatio is " + context2.webkitBackingStorePixelRatio);
-
-            testRunner.notifyDone();
-        });
-    } else {
-        log ("When not run inside DumpRenderTree or WebKitTestRunner, this test just prints the value of");
-        log ("backingStorePixelRatio. Please verify that it matches what you expect, based on the");
-        log ("current configuration.\n");
-        var canvas = document.createElement("canvas");
-        var context = canvas.getContext("2d");
-        log ("context.webkitBackingStorePixelRatio is " + context.webkitBackingStorePixelRatio);
-    }
-</script>