Add base:: to string16s in win8/.

win8/metro_driver/ime/text_service_delegate.h

Index: win8/metro_driver/ime/text_service_delegate.h
diff --git a/win8/metro_driver/ime/text_service_delegate.h b/win8/metro_driver/ime/text_service_delegate.h
index ea9cde72ec5ce4d1a2a688c4e96ed1beefc4611b..9b22a8238ec628880b1ea1c969263845e469ebb4 100644
--- a/win8/metro_driver/ime/text_service_delegate.h
+++ b/win8/metro_driver/ime/text_service_delegate.h
@@ -26,13 +26,13 @@ class TextServiceDelegate {
   // Called when on-going composition is updated. An empty |text| represents
   // that the composition is canceled.
   virtual void OnCompositionChanged(
-      const string16& text,
+      const base::string16& text,
       int32 selection_start,
       int32 selection_end,
       const std::vector<metro_viewer::UnderlineInfo>& underlines) = 0;
 
   // Called when |text| is committed.
-  virtual void OnTextCommitted(const string16& text) = 0;
+  virtual void OnTextCommitted(const base::string16& text) = 0;
 };
 
 }  // namespace metro_driver