Add default zoom functionality to chrome.tabs Zoom API.

chrome/common/extensions/docs/examples/api/tabs/zoom/popup.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.
 
 /**
  * @fileoverview This code supports the popup behaviour of the extension, and
  *               demonstrates how to:
  *
  *               1) Set the zoom for a tab using tabs.setZoom()
  *               2) Read the current zoom of a tab using tabs.getZoom()
@@ skipping 31 matching lines @@
       for (var i = 0; i < modeRadios.length; i++) {
         if (modeRadios[i].value == zoomSettings.mode)
           modeRadios[i].checked = true;
       }
 
       var scopeRadios = document.getElementsByName('scopeRadio');
       for (var i = 0; i < scopeRadios.length; i++) {
         if (scopeRadios[i].value == zoomSettings.scope)
           scopeRadios[i].checked = true;
       }
+
+      var percentDefaultZoom =
+          parseFloat(zoomSettings.default_zoom_factor) * 100;
+      document.getElementById('defaultLabel').textContent =
+          'Default: ' + percentDefaultZoom.toFixed(1) + '%';
     });
 
     chrome.tabs.getZoom(tabId, displayZoomLevel);
   });
 
   document.getElementById('increaseButton').onclick = doZoomIn;
   document.getElementById('decreaseButton').onclick = doZoomOut;
   document.getElementById('defaultButton').onclick = doZoomDefault;
   document.getElementById('setModeButton').onclick = doSetMode;
   document.getElementById('closeButton').onclick = doClose;
@@ skipping 23 matching lines @@
 }
 
 function doZoomOut() {
   changeZoomByFactorDelta(1.0/zoomStep);
 }
 
 function doZoomDefault() {
   if (tabId == -1)
     return;
 
-  chrome.tabs.setZoom(tabId, 1.0, function() {
+  chrome.tabs.setZoom(tabId, 0, function() {
     if (chrome.runtime.lastError)
       console.log('[ZoomDemoExtension] ' + chrome.runtime.lastError.message);
   });
 }
 
 function doSetMode() {
   if (tabId == -1)
     return;
 
   var modeVal;
@@ skipping 21 matching lines @@
       if (chrome.runtime.lastError) {
         console.log('[ZoomDemoExtension] doSetMode() error: ' +
                     chrome.runtime.lastError.message);
       }
     });
 }
 
 function doClose() {
   self.close();
 }