Fix computation of scroll amount in scroll actions.

telemetry/telemetry/internal/actions/drag.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file provides the DragAction object, which performs drag on a page
 // using given start and end positions:
 //   1. var action = new __DragAction(callback)
 //   2. action.start(drag_options)
 'use strict';
 
 (function() {
   function DragGestureOptions(opt_options) {
-      this.element_ = opt_options.element;
-      this.left_start_ratio_ = opt_options.left_start_ratio;
-      this.top_start_ratio_ = opt_options.top_start_ratio;
-      this.left_end_ratio_ = opt_options.left_end_ratio;
-      this.top_end_ratio_ = opt_options.top_end_ratio;
-      this.speed_ = opt_options.speed;
-      this.gesture_source_type_ = opt_options.gesture_source_type;
+    this.element_ = opt_options.element;
+    this.left_start_ratio_ = opt_options.left_start_ratio;
+    this.top_start_ratio_ = opt_options.top_start_ratio;
+    this.left_end_ratio_ = opt_options.left_end_ratio;
+    this.top_end_ratio_ = opt_options.top_end_ratio;
+    this.speed_ = opt_options.speed;
+    this.gesture_source_type_ = opt_options.gesture_source_type;
   }
 
   function supportedByBrowser() {
     return !!(window.chrome &&
               chrome.gpuBenchmarking &&
-              chrome.gpuBenchmarking.smoothDrag);
+              chrome.gpuBenchmarking.smoothDrag &&
+              chrome.gpuBenchmarking.visualViewportHeight &&
+              chrome.gpuBenchmarking.visualViewportWidth);
   }
 
   // This class performs drag action using given start and end positions,
   // by a single drag gesture.
   function DragAction(opt_callback) {
-    this.beginMeasuringHook = function() {}
-    this.endMeasuringHook = function() {}
+    this.beginMeasuringHook = function() {};
+    this.endMeasuringHook = function() {};
 
     this.callback_ = opt_callback;
   }
 
   DragAction.prototype.start = function(opt_options) {
     this.options_ = new DragGestureOptions(opt_options);
     requestAnimationFrame(this.startGesture_.bind(this));
   };
 
   DragAction.prototype.startGesture_ = function() {
@@ skipping 18 matching lines @@
     this.endMeasuringHook();
 
     // We're done.
     if (this.callback_)
       this.callback_();
   };
 
   window.__DragAction = DragAction;
   window.__DragAction_SupportedByBrowser = supportedByBrowser;
 })();