Split BrowserThread into public API and private implementation, step 1.

content/browser/browser_main.h

Index: content/browser/browser_main.h
diff --git a/content/browser/browser_main.h b/content/browser/browser_main.h
index ec1121fec7792995fe79384a59175f05a2606dfa..8b6d3a0181848c6faccea65e7721294be9283bd5 100644
--- a/content/browser/browser_main.h
+++ b/content/browser/browser_main.h
@@ -10,7 +10,6 @@
 #include "base/memory/scoped_ptr.h"
 #include "content/common/content_export.h"
 
-class BrowserThread;
 class CommandLine;
 class HighResolutionTimerManager;
 class MessageLoop;
@@ -20,6 +19,10 @@ namespace base {
 class SystemMonitor;
 }
 
+namespace content {
+class BrowserThreadImpl;
+}
+
 namespace net {
 class NetworkChangeNotifier;
 }
@@ -120,7 +123,7 @@ class CONTENT_EXPORT BrowserMainParts {
   scoped_ptr<base::SystemMonitor> system_monitor_;
   scoped_ptr<HighResolutionTimerManager> hi_res_timer_manager_;
   scoped_ptr<net::NetworkChangeNotifier> network_change_notifier_;
-  scoped_ptr<BrowserThread> main_thread_;
+  scoped_ptr<BrowserThreadImpl> main_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserMainParts);
 };