Bug 1023020 - Add a "ready" promise to canvas graphs, r=pbrosset

browser/devtools/shared/test/browser_graphs-01.js

@@ -20,7 +20,12 @@ function* performTest() {
   doc.body.setAttribute("style", "position: fixed; width: 100%; height: 100%; margin: 0;");
 
   let graph = new LineGraphWidget(doc.body, "fps");
-  yield graph.once("ready");
+
+  let readyEventEmitted;
+  graph.once("ready", () => readyEventEmitted = true);
+
+  yield graph.ready();
+  ok(readyEventEmitted, "The 'ready' event should have been emitted");
 
   testGraph(host, graph);
 

browser/devtools/shared/widgets/Graphs.jsm

@@ -5,8 +5,9 @@
 
 const Cu = Components.utils;
 
-Cu.import("resource://gre/modules/devtools/event-emitter.js");
 Cu.import("resource:///modules/devtools/ViewHelpers.jsm");
+const promise = Cu.import("resource://gre/modules/Promise.jsm", {}).Promise;
+const {EventEmitter} = Cu.import("resource://gre/modules/devtools/event-emitter.js", {});
 
 this.EXPORTED_SYMBOLS = ["LineGraphWidget"];
 
@@ -116,6 +117,7 @@ GraphSelectionResizer.prototype = {
 this.AbstractCanvasGraph = function(parent, name, sharpness) {
   EventEmitter.decorate(this);
 
+  this._ready = promise.defer();
   this._parent = parent;
   this._uid = "canvas-graph-" + Date.now();
 
@@ -165,6 +167,7 @@ this.AbstractCanvasGraph = function(parent, name, sharpness) {
 
     this._animationId = this._window.requestAnimationFrame(this._onAnimationFrame);
 
+    this._ready.resolve(this);
     this.emit("ready", this);
   });
 }
@@ -181,6 +184,13 @@ AbstractCanvasGraph.prototype = {
     return this._height;
   },
 
+  /**
+   * Returns a promise resolved once this graph is ready to receive data.
+   */
+  ready: function() {
+    return this._ready.promise;
+  },
+
   /**
    * Destroys this graph.
    */