Add extension API test for FileSystem API.

chrome/test/data/extensions/api_test/fileapi/background.html

+<script>
+  var fileSystem = null;
+
+  console.log("Requesting a filesystem...");
+  requestFileSystem(window.TEMPORARY, 100, getFileSystem, errorCallback);
+
+  function getFileSystem(fs) {
+    fileSystem = fs;
+    console.log("DONE requesting filesystem: " + fileSystem.name);
+    fileSystem.root.getDirectory('dir', {create:true},

[ericu, 2010/12/01 00:58:46]

Is there ever any cleanup done between tests?  Could this be sitting around from
a previous run?

I'm not sure it matters; we're still demonstrating API access, just not that we
can do something that increases quota usage.

[kinuko, 2010/12/01 03:18:00]

Once we add ExtensionDataDeleter I believe the data goes away between tests.

Meanwhile I also added local clean-up code in tab.html.
(background.html and tab.html usually have different execution timings (when
it's facing users) and I was not sure if creating a file in background.html and
deleting it in tab.html is a good idea.)

+                                 directoryCallback, errorCallback);
+  }
+
+  function directoryCallback(directory) {
+    console.log("DONE creating directory: " + directory.path);
+    directory.getFile('file', {create:true}, fileCallback, errorCallback);
+  }
+
+  function fileCallback(file) {
+    console.log("DONE creating file: " + file.path);
+
+    // See if we get the same filesystem space in the tab.
+    console.log("Opening tab...");
+    chrome.tabs.create({
+      url: "tab.html"
+    });
+  }
+
+  function errorCallback(error) {
+    chrome.test.fail("Got unexpected error: " + error.code);
+  }
+</script>