[NaCl SDK] Screen capture extension for use with SDK visual testing.

native_client_sdk/src/build_tools/screenshot_extension/injected.js

+// Copyright (c) 2013 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.
+
+// Only inject once.
+if (!document.body.getAttribute('screenshot_extension_injected')) {
+  document.body.setAttribute('screenshot_extension_injected', true);
+  (function() {
+
+    // Bounce message from webpage to background page.
+    //
+    // Expecting a message called with:
+    // window.postMessage({
+    //    id: <a value that is passed back unchanged to the response for
+    //         identification>,
+    //    target: 'background'
+    // }, '*');
+    //
+    // When the screenshot is captured, a message will be posted to the window.
+    // Listen for it like this:
+    //
+    // window.addEventListener('message', function(event) {
+    //   if (event.source !== window)
+    //     return;
+    //
+    //   if (event.data.target !== 'page')
+    //     return;
+    //
+    //   // event.data is an object:
+    //   // {
+    //   //   id: <the id passed to the request>,
+    //   //   target: 'page',
+    //   //   data: <a data URI of MIMEtype image/png with the tab screenshot>
+    //   // }
+    //   //
+    //   // or if there is an error:
+    //   //
+    //   // {
+    //   //   id: <the id passed to the request>,
+    //   //   target: 'page',
+    //   //   error: <an error string>
+    //   // }
+    // }, false);
+    //
+    window.addEventListener('message', function(event) {
+      if (event.source !== window)
+        return;
+
+      // Ignore messages not destined for the background page.
+      if (event.data.target !== 'background')
+        return;
+
+      var id = event.data.id;
+      console.log('sending message: id=' + id);
+
+      chrome.runtime.sendMessage(null, {},
+          function(responseData) {
+            // Bounce response from background page back to webpage.
+            var lastError = chrome.runtime.lastError;
+            if (lastError) {
+              console.log('lastError: ' + lastError);
+
+              window.postMessage({id: id, target: 'page', error: lastError},
+                                 '*');
+              return;
+            }
+
+            console.log('received response: id=' + id);
+
+            window.postMessage({id: id, target: 'page', data: responseData},
+                               '*');
+      });
+    }, false);
+  })();
+}