PNaCl on-demand installs: Make a separate async IPC to check if PNaCl is installed

chrome/browser/nacl_host/nacl_file_host.h

Index: chrome/browser/nacl_host/nacl_file_host.h
diff --git a/chrome/browser/nacl_host/nacl_file_host.h b/chrome/browser/nacl_host/nacl_file_host.h
index ee473cc3de0ab941e04f8a1b238a1ae3f4a9cade..2f1284e9eeb79aeb78a6c25932d955184edd759a 100644
--- a/chrome/browser/nacl_host/nacl_file_host.h
+++ b/chrome/browser/nacl_host/nacl_file_host.h
@@ -25,8 +25,19 @@ class Message;
 // Opens NaCl Files in the Browser process, on behalf of the NaCl plugin.
 
 namespace nacl_file_host {
-
-// Open a Pnacl file (readonly) on behalf of the NaCl plugin.
+typedef base::Callback<void(bool)> InstallCallback;
+typedef base::Callback<void(int64_t, int64_t)> InstallProgressCallback;
+
+// Ensure that PNaCl is installed.  Calls |done_callback| if PNaCl is already
+// installed.  Otherwise, issues a request to install and calls |done_callback|
+// after that request completes w/ success or failure.
+// If an request to install is issued, then |progress_callback| is called
+// with progress updates.
+void EnsurePnaclInstalled(
+    const InstallCallback& done_callback,
+    const InstallProgressCallback& progress_callback);
+
+// Open a PNaCl file (readonly) on behalf of the NaCl plugin.
 void GetReadonlyPnaclFd(
     scoped_refptr<NaClHostMessageFilter> nacl_host_message_filter,
     const std::string& filename,