[Devtools] Changed once to emit a promise instead of using callback

Moves to use a promise instead of a callback for event emitable items.

R=dgozman
BUG=None

Change-Id: I1d4cd1084127d73d9ed96a9dddcef1e0d8a5fe7d
Reviewed-on: https://chromium-review.googlesource.com/527660
Commit-Queue: Alexei Filippov <alph@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#478825}

third_party/WebKit/LayoutTests/http/tests/inspector/inspector-test.js

@@ -475,7 +475,7 @@ InspectorTest.waitForUISourceCode = function(urlSuffix, projectType)
 
 InspectorTest.waitForUISourceCodeRemoved = function(callback)
 {
-    InspectorTest.waitForEvent(Workspace.Workspace.Events.UISourceCodeRemoved, Workspace.workspace).then(callback);
+    Workspace.workspace.once(Workspace.Workspace.Events.UISourceCodeRemoved).then(callback);
 }
 
 InspectorTest.waitForTarget = function(filter) {
@@ -503,7 +503,7 @@ InspectorTest.waitForTarget = function(filter) {
 InspectorTest.waitForExecutionContext = function(runtimeModel) {
     if (runtimeModel.executionContexts().length)
         return Promise.resolve(runtimeModel.executionContexts()[0]);
-    return InspectorTest.waitForEvent(SDK.RuntimeModel.Events.ExecutionContextCreated, runtimeModel);
+    return runtimeModel.once(SDK.RuntimeModel.Events.ExecutionContextCreated);
 }
 
 InspectorTest.waitForExecutionContextDestroyed = function(context) {

third_party/WebKit/Source/devtools/front_end/audits2/Audits2Panel.js

@@ -750,9 +750,7 @@ Audits2.DetailsRenderer = class extends DetailsRenderer {
     var mainTarget = SDK.targetManager.mainTarget();
     if (!this._onMainFrameNavigatedPromise) {
       var resourceTreeModel = mainTarget.model(SDK.ResourceTreeModel);
-      this._onMainFrameNavigatedPromise = new Promise(resolve => {
-        resourceTreeModel.once(SDK.ResourceTreeModel.Events.MainFrameNavigated, resolve);
-      });
+      this._onMainFrameNavigatedPromise = resourceTreeModel.once(SDK.ResourceTreeModel.Events.MainFrameNavigated);
     }
 
     await this._onMainFrameNavigatedPromise;

third_party/WebKit/Source/devtools/front_end/common/Object.js

@@ -56,21 +56,15 @@ Common.Object = class {
   /**
    * @override
    * @param {symbol} eventType
-   * @param {function(!Common.Event)} listener
-   * @param {!Object=} thisObject
-   * @return {!Common.EventTarget.EventDescriptor}
+   * @return {!Promise<*>}
    */
-  once(eventType, listener, thisObject) {
-    /**
-     * @this {Common.Object}
-     * @param {!Common.Event} event
-     */
-    function onEvent(event) {
-      listener.call(thisObject, event);
-      this.removeEventListener(eventType, onEventBound, thisObject);
-    }
-    var onEventBound = onEvent.bind(this);
-    return this.addEventListener(eventType, onEventBound, thisObject);
+  once(eventType) {
+    return new Promise(resolve => {
+      var descriptor = this.addEventListener(eventType, event => {
+        this.removeEventListener(eventType, descriptor.listener);
+        resolve(event.data);
+      });
+    });
   }
 
   /**
@@ -162,11 +156,9 @@ Common.EventTarget.prototype = {
 
   /**
    * @param {symbol} eventType
-   * @param {function(!Common.Event)} listener
-   * @param {!Object=} thisObject
-   * @return {!Common.EventTarget.EventDescriptor}
+   * @return {!Promise<*>}
    */
-  once(eventType, listener, thisObject) {},
+  once(eventType) {},
 
   /**
    * @param {symbol} eventType