Move Singleton and related structs to namespace base

chrome/browser/speech/tts_mac.mm

Index: chrome/browser/speech/tts_mac.mm
diff --git a/chrome/browser/speech/tts_mac.mm b/chrome/browser/speech/tts_mac.mm
index 21aa9a23dd8138d9132a14873cb449c6dc632a0e..a492dd54c4772a28af521f86c517d3a9b4ea0a6e 100644
--- a/chrome/browser/speech/tts_mac.mm
+++ b/chrome/browser/speech/tts_mac.mm
@@ -89,7 +89,7 @@ class TtsPlatformImplMac : public TtsPlatformImpl {
   int last_char_index_;
   bool paused_;
 
-  friend struct DefaultSingletonTraits<TtsPlatformImplMac>;
+  friend struct base::DefaultSingletonTraits<TtsPlatformImplMac>;
 
   DISALLOW_COPY_AND_ASSIGN(TtsPlatformImplMac);
 };
@@ -289,7 +289,7 @@ TtsPlatformImplMac::~TtsPlatformImplMac() {
 
 // static
 TtsPlatformImplMac* TtsPlatformImplMac::GetInstance() {
-  return Singleton<TtsPlatformImplMac>::get();
+  return base::Singleton<TtsPlatformImplMac>::get();
 }
 
 @implementation ChromeTtsDelegate