Added new fileBrowserPrivate and fileHandler extension APIs

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

+<script>
+// Context menu hanler method.
+function onRunContextMenuHandler() {
+  return function(info, tab) {
+    // Create a new tab
+    chrome.tabs.create({
+      url: "tab.html#" + info.srcUrl
+    });
+  };
+};
+
+
+chrome.test.runTests([function tab() {
+  // Register a context menu (file intent) handler.
+  chrome.contextMenus.create({
+    "title" : "Magic File Task",
+    "type" : "normal",
+    "targetUrlPatterns" : ["filesystem:*.txt" ],
+    "contexts" : ["file"],
+    "onclick" : onRunContextMenuHandler()
+  });
+  // Finish this test.
+  console.log("Registered contect menu handler.");
+  chrome.test.succeed();
+}]);
+
+</script>