Extensions docs, declarativeWebRequest: notice being on hold

Because Declarative Web Request lacks an active owner at the moment, this CL adds a warning notice to the API's documentation site:
"this API is currently on hold, without concrete plans to move to stable"

Staged at https://chrome-apps-doc.appspot.com/_patch/276483005/extensions/declarativeWebRequest, but http://crbug.com/371402. Screenshots in my GDrive: https://drive.google.com/a/google.com/folderview?id=0Bx9cneu-k1RNeUZnRk5NWERObE0&usp=sharing (Google only, but let me know if you come from outside and need them).

Original at https://developer.chrome.com/extensions/declarativeWebRequest

BUG=112155

Review URL: https://codereview.chromium.org/276483005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269567 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/api/declarative_web_request.json

@@ -5,7 +5,7 @@
 [
   {
     "namespace": "declarativeWebRequest",
-    "description": "Use the <code>chrome.declarativeWebRequest</code> API to intercept, block, or modify requests in-flight. It is significantly faster than the <a href='webRequest.html'><code>chrome.webRequest</code> API</a> because you can register rules that are evaluated in the browser rather than the JavaScript engine with reduces roundtrip latencies and allows higher efficiency.",
+    "description": "<em><strong>Note:</strong> this API is currently on hold, without concrete plans to move to stable.</em> Use the <code>chrome.declarativeWebRequest</code> API to intercept, block, or modify requests in-flight. It is significantly faster than the <a href='webRequest.html'><code>chrome.webRequest</code> API</a> because you can register rules that are evaluated in the browser rather than the JavaScript engine with reduces roundtrip latencies and allows higher efficiency.",
     "types": [
       {
         "id": "HeaderFilter",