Add a NaCl-Private interface for opening files in DIR_PNACL_COMPONENT.

ppapi/api/private/finish_writing_these/ppb_nacl_private.idl

Index: ppapi/api/private/finish_writing_these/ppb_nacl_private.idl
diff --git a/ppapi/api/private/finish_writing_these/ppb_nacl_private.idl b/ppapi/api/private/finish_writing_these/ppb_nacl_private.idl
index e9047d228c16901327d1c1c539ff38f0ec2c942f..e92d9b8c1a86df2da1baad2599f2efb61c194729 100644
--- a/ppapi/api/private/finish_writing_these/ppb_nacl_private.idl
+++ b/ppapi/api/private/finish_writing_these/ppb_nacl_private.idl
@@ -31,4 +31,11 @@ interface PPB_NaCl_Private_0_5 {
    * code to be processed by the graphics stack.
    */
   bool Are3DInterfacesDisabled();
+
+  /* Returns a read-only file descriptor of a file rooted in the Pnacl
+   * component directory, or -1 on error.
+   * Do we want this to take a completion callback and be async, or
+   * could we make this happen on another thread?
+   */
+  int32_t GetReadonlyPnaclFd([in] str_t filename);
 };