Fix computation of scroll amount in scroll actions.

telemetry/telemetry/internal/actions/drag.js

Index: telemetry/telemetry/internal/actions/drag.js
diff --git a/telemetry/telemetry/internal/actions/drag.js b/telemetry/telemetry/internal/actions/drag.js
index cee51ae9e9c2b410b51945cf5dd1d21e51a9dbec..8c5613c955c249a1c6df1805b56db74f80828df7 100644
--- a/telemetry/telemetry/internal/actions/drag.js
+++ b/telemetry/telemetry/internal/actions/drag.js
@@ -10,26 +10,28 @@
 
 (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;
   }