Add a Flash API to get the device ID.

ppapi/api/private/ppb_flash.idl

Index: ppapi/api/private/ppb_flash.idl
diff --git a/ppapi/api/private/ppb_flash.idl b/ppapi/api/private/ppb_flash.idl
index 997274e8a06a867d02915ff768f0b8edd458e1cc..b0838828a6dfce08173aa06e9423b9075b88eb22 100644
--- a/ppapi/api/private/ppb_flash.idl
+++ b/ppapi/api/private/ppb_flash.idl
@@ -9,7 +9,8 @@
 
 label Chrome {
   M17 = 12.0,
-  M19 = 12.1
+  M19 = 12.1,
+  M20 = 12.2
 };
 
 /**
@@ -129,6 +130,12 @@ interface PPB_Flash {
   [version=12.1]
   void UpdateActivity(
       [in] PP_Instance instance);
+
+  /**
+   * Returns the device ID as a string. Returns a PP_VARTYPE_UNDEFINED on error.
+   */
+  [version=12.2]
+  PP_Var GetDeviceID([in] PP_Instance instance);
 };
 
 #inline c