Cause the viewport to fit to the PDF document width on load

chrome/browser/resources/pdf/viewport.js

 // Copyright 2014 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.
 
 /**
  * Returns the area of the intersection of two rectangles.
  * @param {Object} rect1 the first rect
  * @param {Object} rect2 the second rect
  * @return {number} the area of the intersection of the rects
  */
@@ skipping 403 matching lines @@
       page = this.pageDimensions_.length - 1;
     var dimensions = this.pageDimensions_[page];
     this.window_.scrollTo(dimensions.x * this.zoom_, dimensions.y * this.zoom_);
   },
 
   /**
    * Set the dimensions of the document.
    * @param {Object} documentDimensions the dimensions of the document
    */
   setDocumentDimensions: function(documentDimensions) {
+    var initialDimensions = !this.documentDimensions_;
     this.documentDimensions_ = documentDimensions;
     this.pageDimensions_ = this.documentDimensions_.pageDimensions;
+    if (initialDimensions) {
+      this.setZoom_(this.computeFittingZoom_(this.documentDimensions_, true));
+      if (this.zoom_ > 1)
+        this.setZoom_(1);
+      this.window_.scrollTo(0, 0);
+    }
     this.contentSizeChanged_();
     this.resize_();
   },
 
   /**
    * Get the coordinates of the page contents (excluding the page shadow)
    * relative to the screen.
    * @param {number} page the index of the page to get the rect for.
    * @return {Object} a rect representing the page in screen coordinates.
    */
@@ skipping 18 matching lines @@
         (this.size.width - pageDimensions.width * this.zoom_) / 2.0, 0);
 
     return {
       x: Viewport.PAGE_SHADOW.left + spaceOnLeft - this.window_.pageXOffset,
       y: (insetDimensions.y * this.zoom_) - this.window_.pageYOffset,
       width: insetDimensions.width * this.zoom_,
       height: insetDimensions.height * this.zoom_
     };
   }
 };