Add base:: to string16s in win8/.

win8/metro_driver/ime/text_store_delegate.h

Index: win8/metro_driver/ime/text_store_delegate.h
diff --git a/win8/metro_driver/ime/text_store_delegate.h b/win8/metro_driver/ime/text_store_delegate.h
index af06516471467817b835bdb9caae1483c29e6949..153d664f4ead307acb5276bf181f3ef1c9aeb015 100644
--- a/win8/metro_driver/ime/text_store_delegate.h
+++ b/win8/metro_driver/ime/text_store_delegate.h
@@ -30,13 +30,13 @@ class TextStoreDelegate {
   // 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;
 
   // Called when an IME requests the caret position. Objects that implement
   // this method must return the caret position in screen coordinates.