Added new fileBrowserPrivate and fileHandler extension APIs

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

+<script>
+var last_file_entries = null;
+
+function getLastFileEntries() {
+  return last_file_entries;
+}
+
+chrome.fileBrowserHandler.onExecute.addListener(
+  function(id, file_entries) {
+    if (id != "TestAction") {
+      chrome.test.fail("Unexpected action id: " + id);
+      return;
+    }
+    if (!file_entries || file_entries.length != 1) {
+      chrome.test.fail("Unexpected file url list");
+      return;
+    }
+    last_file_entries = file_entries;
+    // Create a new tab
+    chrome.tabs.create({
+      url: "tab.html"
+    });
+  });
+
+chrome.test.succeed();
+
+</script>