Fix some typos, broken links and other issues in extension docs

chrome/common/extensions/docs/templates/articles/content_scripts.html

 <h1>Content Scripts</h1>
 
 
 <p>
 Content scripts are JavaScript files that run in the context of web pages.
 By using the standard
 <a href="http://www.w3.org/TR/DOM-Level-2-HTML/">Document
 Object Model</a> (DOM),
 they can read details of the web pages the browser visits,
 or make changes to them.
@@ skipping 64 matching lines @@
       "css": ["mystyles.css"],
       "js": ["jquery.js", "myscript.js"]
     }
   ]</b>,
   ...
 }</pre>
 
 <p>
 If you want to inject the code only sometimes,
 use the
-<a href="manifest.html#permissions"><code>permissions</code></a> field instead,
+<a href="declare_permissions.html"><code>permissions</code></a> field instead,
 as described in <a href="#pi">Programmatic injection</a>.
 </p>
 
 <pre>{
   "name": "My extension",
   ...
   <b>"permissions": [
     "tabs", "http://www.google.com/*"
   ]</b>,
   ...
@@ skipping 143 matching lines @@
 </p>
 
 <p>
 To insert code into a page,
 your extension must have
 <a href="xhr.html#requesting-permission">cross-origin permissions</a>
 for the page.
 It also must be able to use the <code>chrome.tabs</code> module.
 You can get both kinds of permission
 using the manifest file's
-<a href="manifest.html#permissions">permissions</a> field.
+<a href="declare_permissions.html">permissions</a> field.
 </p>
 
 <p>
 Once you have permissions set up,
 you can inject JavaScript into a page by calling
 $ref:tabs.executeScript.
 To inject CSS, use
 $ref:tabs.insertCSS.
 </p>
 
@@ skipping 100 matching lines @@
     window.postMessage({ type: "FROM_PAGE", text: "Hello from the webpage!" }, "*");
 }, false);</pre>
 <p>In the above example, example.html (which is not a part of the extension) posts messages to itself, which are intercepted and inspected by the content script, and then posted to the extension process. In this way, the page establishes a line of communication to the extension process. The reverse is possible through similar means.</p>
 
 <h2 id="security-considerations">Security considerations</h2>
 
 <p>When writing a content script, you should be aware of two security issues.
 First, be careful not to introduce security vulnerabilities into the web site
 your content script is injected into.  For example, if your content script
 receives content from another web site (for example, by making an <a
-href="messaging.html">XMLHttpRequest</a>),
+href="xhr.html">XMLHttpRequest</a>),
 be careful to filter that content for <a
 href="http://en.wikipedia.org/wiki/Cross-site_scripting">cross-site
 scripting</a> attacks before injecting the content into the current page.
 For example, prefer to inject content via innerText rather than innerHTML.
 Be especially careful when retrieving HTTP content on an HTTPS page because
 the HTTP content might have been corrupted by a network <a
 href="http://en.wikipedia.org/wiki/Man-in-the-middle_attack">"man-in-the-middle"</a>
 if the user is on a hostile network.</p>
 
 <p>Second, although running your content script in an isolated world provides
@@ skipping 71 matching lines @@
 
 <p>
 The next video describes message passing,
 featuring an example of a content script
 sending a request to its parent extension.
 </p>
 
 <p>
 <iframe title="YouTube video player" width="640" height="390" src="http://www.youtube.com/embed/B4M_a7xejYI?rel=0" frameborder="0" allowfullscreen></iframe>
 </p>