Add a "minimum_chrome_version" key to the manifest.

chrome/common/extensions/docs/static/manifest.html

 <div id="pageData-name" class="pageData">Formats: Manifest Files</div>
 <div id="pageData-showTOC" class="pageData">true</div>
 
 <p>
 Every extension has a
 <a href="http://www.json.org">JSON</a>-formatted manifest file,
 named <code>manifest.json</code>,
 that provides important information about the extension.
 </p>
 
@@ skipping 18 matching lines @@
 
   <em>// Pick one (or none)</em>
   "<a href="browserAction.html">browser_action</a>": {...},
   "<a href="pageAction.html">page_action</a>": {...},
   "<a href="themes.html">theme</a>": {...},
 
   <em>// Add any of these that you need</em>
   "<a href="background_pages.html">background_page</a>": "<em>aFile</em>.html",
   "<a href="override.html">chrome_url_overrides</a>": {...},
   "<a href="content_scripts.html">content_scripts</a>": [...],
+  "<a href="#minimum_chrome_version">minimum_chrome_version</a>": "x.y",
   "<a href="options.html">options_page</a>": "<em>aFile</em>.html",
   "<a href="#permissions">permissions</a>": [...],
   "<a href="npapi.html">plugins</a>": [...],
   "<a href="autoupdate.html">update_url</a>": "http://<em>path/to/updateInfo</em>.xml"
 }
 </pre>
 
 
 <h2>Field details</h2>
 
@@ skipping 56 matching lines @@
 
 <p>
 A short, plain text string
 (no more than 45 characters)
 that identifies the extension.
 The name is used in the install dialog,
 extension management UI,
 and the <a href="https://chrome.google.com/extensions">extension gallery</a>.
 </p>
 
+<h3 id="minimum_chrome_version">Minimum Chrome Version</h3>
+
+<p>
+The version of Google Chrome that your extension requires, if any.
+The format for this string is the same as for the <a href="#version">version
+field</a>.
+
 <h3 id="permissions">permissions</h3>
 
 <p>
 An array of permissions that the extension might use.
 Each permission can be either one of a list of known strings
 (such as "tabs" or "bookmarks")
 or a match pattern
 that gives access to one or more hosts.
 These permissions are displayed to users before installation.
 Permissions might also help to limit damage
@@ skipping 73 matching lines @@
 A missing integer is equal to zero.
 For example, 1.1.9.9999 is newer than 1.1.
 </p>
 
 <p>
 For more information, see
 <a href="autoupdate.html">Autoupdating</a>.
 </p>
 
 <!-- [PENDING: Possibly: point to the gallery and make a big deal of the fact that autoupdating is free if you use the gallery.] -->