added canvas_helper file

translator/testFiles/canvas_helper.js

@@ -0,0 +1,15 @@
+function getContext() {
+    return document.getElementsByTagName('canvas')[0].getContext('2d');
+}
+
+function random() {
+    return Math.random();
+}
+
+function getCanvasWidth() {
+    return document.getElementsByTagName('canvas')[0].width;
+}
+
+function getCanvasHeight() {
+    return document.getElementsByTagName('canvas')[0].height;
+}