Stretching NativeViewHost, and misc tab capture fixes.

chrome/common/extensions/docs/examples/api/tabCapture/eventPage.js

 // Copyright 2016 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.
 
 // The window (tab) opened and navigated to receiver.html.
 var receiver = null;
 
 // Open a new window of receiver.html when browser action icon is clicked.
 chrome.browserAction.onClicked.addListener(function(tab) {
   chrome.tabCapture.capture(
     {video: true, audio: true,
      videoConstraints: {
        mandatory: {
          // If minWidth/Height have the same aspect ratio (e.g., 16:9) as
          // maxWidth/Height, the implementation will letterbox/pillarbox as
          // needed. Otherwise, set minWidth/Height to 0 to allow output video
          // to be of any arbitrary size.
          minWidth: 16,
          minHeight: 9,
-         maxWidth: 854,
-         maxHeight: 480,
+         maxWidth: 1280,
+         maxHeight: 720,
          maxFrameRate: 60,  // Note: Frame rate is variable (0 <= x <= 60).
        },
      },
     },
     function(stream) {
       if (!stream) {
         console.error('Error starting tab capture: ' +
                       (chrome.runtime.lastError.message || 'UNKNOWN'));
         return;
       }
       if (receiver != null) {
         receiver.close();
       }
       receiver = window.open('receiver.html');
       receiver.currentStream = stream;
     }
   );
 });