Use base namespace for string16 in chrome/renderer.

chrome/renderer/spellchecker/spelling_engine.h

Index: chrome/renderer/spellchecker/spelling_engine.h
diff --git a/chrome/renderer/spellchecker/spelling_engine.h b/chrome/renderer/spellchecker/spelling_engine.h
index 7deb816b62bfa5e68313e5fac5b6b109441a5e57..f6e6bff600ee0486f2e5ee465076dbd575793f15 100644
--- a/chrome/renderer/spellchecker/spelling_engine.h
+++ b/chrome/renderer/spellchecker/spelling_engine.h
@@ -24,10 +24,10 @@ class SpellingEngine {
   virtual void Init(base::PlatformFile bdict_file) = 0;
   virtual bool InitializeIfNeeded() = 0;
   virtual bool IsEnabled() = 0;
-  virtual bool CheckSpelling(const string16& word_to_check, int tag) = 0;
+  virtual bool CheckSpelling(const base::string16& word_to_check, int tag) = 0;
   virtual void FillSuggestionList(
-      const string16& wrong_word,
-      std::vector<string16>* optional_suggestions) = 0;
+      const base::string16& wrong_word,
+      std::vector<base::string16>* optional_suggestions) = 0;
 };
 
 #endif  // CHROME_RENDERER_SPELLCHECKER_SPELLING_ENGINE_H_