|  | @@ -658,6 +658,28 @@ function getPDFFileNameFromURL(url) {
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				|  |  |    return suggestedFilename || 'document.pdf';
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				|  |  |  }
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				|  |  |  
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				|  |  | +function normalizeWheelEventDelta(evt) {
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				|  |  | +  var delta = Math.sqrt(evt.deltaX * evt.deltaX + evt.deltaY * evt.deltaY);
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				|  |  | +  var angle = Math.atan2(evt.deltaY, evt.deltaX);
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				|  |  | +  if (-0.25 * Math.PI < angle && angle < 0.75 * Math.PI) {
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				|  |  | +    // All that is left-up oriented has to change the sign.
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				|  |  | +    delta = -delta;
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				|  |  | +  }
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				|  |  | +
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				|  |  | +  var MOUSE_DOM_DELTA_PIXEL_MODE = 0;
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				|  |  | +  var MOUSE_DOM_DELTA_LINE_MODE = 1;
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				|  |  | +  var MOUSE_PIXELS_PER_LINE = 30;
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				|  |  | +  var MOUSE_LINES_PER_PAGE = 30;
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				|  |  | +
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				|  |  | +  // Converts delta to per-page units
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				|  |  | +  if (evt.deltaMode === MOUSE_DOM_DELTA_PIXEL_MODE) {
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				|  |  | +    delta /= MOUSE_PIXELS_PER_LINE * MOUSE_LINES_PER_PAGE;
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				|  |  | +  } else if (evt.deltaMode === MOUSE_DOM_DELTA_LINE_MODE) {
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				|  |  | +    delta /= MOUSE_LINES_PER_PAGE;
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				|  |  | +  }
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				|  |  | +  return delta;
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				|  |  | +}
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				|  |  | +
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				|  |  |  /**
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				|  |  |   * Simple event bus for an application. Listeners are attached using the
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				|  |  |   * `on` and `off` methods. To raise an event, the `dispatch` method shall be
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				|  | @@ -803,6 +825,7 @@ exports.getOutputScale = getOutputScale;
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				|  |  |  exports.scrollIntoView = scrollIntoView;
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				|  |  |  exports.watchScroll = watchScroll;
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				|  |  |  exports.binarySearchFirstItem = binarySearchFirstItem;
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				|  |  | +exports.normalizeWheelEventDelta = normalizeWheelEventDelta;
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				|  |  |  }));
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				|  |  |  
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				|  |  |  
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