Type check PDF plugin JS code, down to 53 errors.

chrome/browser/resources/pdf/viewport_scroller.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.
 
 'use strict';
 
 /**
  * @private
  * The period of time in milliseconds to wait between updating the viewport
  * position by the scroll velocity.
  */
 ViewportScroller.DRAG_TIMER_INTERVAL_MS_ = 100;
 
 /**
  * @private
  * The maximum drag scroll distance per DRAG_TIMER_INTERVAL in pixels.
  */
 ViewportScroller.MAX_DRAG_SCROLL_DISTANCE_ = 100;
 
 /**
  * Creates a new ViewportScroller.
  * A ViewportScroller scrolls the page in response to drag selection with the
  * mouse.
  * @param {Object} viewport The viewport info of the page.
  * @param {Object} plugin The PDF plugin element.
  * @param {Object} window The window containing the viewer.
+ * @constructor
  */
 function ViewportScroller(viewport, plugin, window) {
   this.viewport_ = viewport;
   this.plugin_ = plugin;
   this.window_ = window;
   this.mousemoveCallback_ = null;
   this.timerId_ = null;
   this.scrollVelocity_ = null;
   this.lastFrameTime_ = 0;
 }
@@ skipping 89 matching lines @@
                                     false);
     } else {
       this.stopDragScrollTimer_();
       if (this.mousemoveCallback_) {
         this.plugin_.removeEventListener('mousemove', this.mousemoveCallback_,
                                          false);
       }
     }
   }
 };