Implement declarativeContent API.

chrome/renderer/resources/extensions/content_watcher.js

Index: chrome/renderer/resources/extensions/content_watcher.js
diff --git a/chrome/renderer/resources/extensions/content_watcher.js b/chrome/renderer/resources/extensions/content_watcher.js
new file mode 100644
index 0000000000000000000000000000000000000000..5a3ea61a55d4fbc0b28103a1c3029e5968999b69
--- /dev/null
+++ b/chrome/renderer/resources/extensions/content_watcher.js
@@ -0,0 +1,32 @@
+// Copyright (c) 2012 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.
+
+var contentWatcherNative = requireNative("contentWatcherNative");
+
+// Returns the indices in |css_selectors| that match any element on the page.
+exports.FindMatchingSelectors = function(css_selectors) {
+  result = []
+  css_selectors.forEach(function(selector, index) {
+    try {
+      if (document.querySelector(selector) != null)
+        result.push(index);
+    } catch (exception) {
+      throw new Error("query Selector failed on '" + selector + "': " +
+                      exception.stack);
+    }
+  });
+  return result;
+};
+
+// Watches the page for all changes and calls FrameMutated (a C++ callback) in
+// response.
+var mutation_observer = new WebKitMutationObserver(
+  contentWatcherNative.FrameMutated);
+
+// This runs once per frame, when the module is 'require'd.
+mutation_observer.observe(document, {
+  childList: true,
+  attributes: true,
+  characterData: true,
+  subtree: true});