[filebrowser] Introduce View action for supported file types (e.g. pdf).

chrome/test/data/extensions/api_test/filesystem_handler_write/tab.js

Index: chrome/test/data/extensions/api_test/filesystem_handler_write/tab.js
===================================================================
--- chrome/test/data/extensions/api_test/filesystem_handler_write/tab.js	(revision 125140)
+++ chrome/test/data/extensions/api_test/filesystem_handler_write/tab.js	(working copy)
@@ -93,7 +93,7 @@
 }
 
 function executeListener(id, details) {
-  if (id != "TextAction" && id != "BaseAction" && id != "JpegAction") {
+  if (id != "AbcAction" && id != "BaseAction" && id != "123Action") {
     chrome.test.fail("Unexpected action id: " + id);
     return;
   }