Fix computation of scroll amount in scroll actions.

telemetry/telemetry/internal/actions/pinch.js

 // Copyright 2013 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 PinchAction object, which zooms into or out of a
 // page by a given scale factor:
 //   1. var action = new __PinchAction(callback)
 //   2. action.start(pinch_options)
 'use strict';
 
@@ skipping 11 matching lines @@
       this.left_anchor_ratio_ = 0.5;
       this.top_anchor_ratio_ = 0.5;
       this.scale_factor_ = 2.0;
       this.speed_ = 800;
     }
   }
 
   function supportedByBrowser() {
     return !!(window.chrome &&
               chrome.gpuBenchmarking &&
-              chrome.gpuBenchmarking.pinchBy);
+              chrome.gpuBenchmarking.pinchBy &&
+              chrome.gpuBenchmarking.visualViewportHeight &&
+              chrome.gpuBenchmarking.visualViewportWidth);
   }
 
   // This class zooms into or out of a page, given a number of pixels for
   // the synthetic pinch gesture to cover.
   function PinchAction(opt_callback) {
     var self = this;
 
-    this.beginMeasuringHook = function() {}
-    this.endMeasuringHook = function() {}
+    this.beginMeasuringHook = function() {};
+    this.endMeasuringHook = function() {};
 
     this.callback_ = opt_callback;
   };
 
   PinchAction.prototype.start = function(opt_options) {
     this.options_ = new PinchGestureOptions(opt_options);
 
     requestAnimationFrame(this.startPass_.bind(this));
   };
 
@@ skipping 14 matching lines @@
   PinchAction.prototype.onGestureComplete_ = function() {
     this.endMeasuringHook();
 
     if (this.callback_)
       this.callback_();
   };
 
   window.__PinchAction = PinchAction;
   window.__PinchAction_SupportedByBrowser = supportedByBrowser;
 })();