Add base:: to string16 in extensions/.

extensions/common/permissions/permission_message_provider.h

Index: extensions/common/permissions/permission_message_provider.h
diff --git a/extensions/common/permissions/permission_message_provider.h b/extensions/common/permissions/permission_message_provider.h
index 7f682e3e5de37026462d2a4d3d70cf6bdf9ee515..ab8b49e677288a6fe53ca6b828694dd01daf43c0 100644
--- a/extensions/common/permissions/permission_message_provider.h
+++ b/extensions/common/permissions/permission_message_provider.h
@@ -33,14 +33,14 @@ class PermissionMessageProvider {
 
   // Gets the localized permission messages that represent this set (represented
   // as strings). The set of permission messages shown varies by extension type.
-  virtual std::vector<string16> GetWarningMessages(
+  virtual std::vector<base::string16> GetWarningMessages(
       const PermissionSet* permissions,
       Manifest::Type extension_type) const = 0;
 
   // Gets the localized permission details for messages that represent this set
   // (represented as strings). The set of permission messages shown varies by
   // extension type.
-  virtual std::vector<string16> GetWarningMessagesDetails(
+  virtual std::vector<base::string16> GetWarningMessagesDetails(
       const PermissionSet* permissions,
       Manifest::Type extension_type) const = 0;