PDF: Add shortcut to toggle fit-to-{page,width}.

chrome/browser/resources/pdf/elements/viewer-zoom-toolbar/viewer-zoom-toolbar.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.
 
 (function() {
 
   var FIT_TO_PAGE = 0;
   var FIT_TO_WIDTH = 1;
 
   Polymer({
@@ skipping 20 matching lines @@
      */
     updateTooltips_: function() {
       this.$['fit-button'].tooltips = [
           this.strings.tooltipFitToPage,
           this.strings.tooltipFitToWidth
       ];
       this.$['zoom-in-button'].tooltips = [this.strings.tooltipZoomIn];
       this.$['zoom-out-button'].tooltips = [this.strings.tooltipZoomOut];
     },
 
+    /**
+     * Toggle the state of the fit-button when something external, e.g. the
+     * fit-button equivalent shortcut key, toggles the zoom state.
+     */
+    toggleFitButtonUIState: function() {
+      var button = this.$['fit-button'];
+      if (button.activeIndex == FIT_TO_WIDTH)
+        button.activeIndex = FIT_TO_PAGE;
+      else
+        button.activeIndex = FIT_TO_WIDTH;
+    },
+
+    /**
+     * Handle clicks of the fit-button.
+     */
     fitToggle: function() {
       if (this.$['fit-button'].activeIndex == FIT_TO_WIDTH)
         this.fire('fit-to-width');
       else
         this.fire('fit-to-page');
     },
 
+    /**
+     * Handle clicks of the zoom-in-button.
+     */
     zoomIn: function() {
       this.fire('zoom-in');
     },
 
+    /**
+     * Handle clicks of the zoom-out-button.
+     */
     zoomOut: function() {
       this.fire('zoom-out');
     },
 
     show: function() {
       if (!this.visible_) {
         this.visible_ = true;
         this.$['fit-button'].show();
         this.$['zoom-in-button'].show();
         this.$['zoom-out-button'].show();
       }
     },
 
     hide: function() {
       if (this.visible_) {
         this.visible_ = false;
         this.$['fit-button'].hide();
         this.$['zoom-in-button'].hide();
         this.$['zoom-out-button'].hide();
       }
     },
   });
 
 })();