Have content/ create and destroy its own threads.

content/browser/browser_thread_impl.h

Index: content/browser/browser_thread_impl.h
diff --git a/content/browser/browser_thread_impl.h b/content/browser/browser_thread_impl.h
index e24b385b8642abe71e7b733174277e39c17a38e4..d00ff5b29bbd42dcbebc74c502fd0c8aadb681b8 100644
--- a/content/browser/browser_thread_impl.h
+++ b/content/browser/browser_thread_impl.h
@@ -6,22 +6,33 @@
 #define CONTENT_BROWSER_BROWSER_THREAD_IMPL_H_
 #pragma once
 
+#include "base/synchronization/lock.h"
+#include "base/threading/thread.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace content {
 
-class CONTENT_EXPORT BrowserThreadImpl : public BrowserThread {
+class CONTENT_EXPORT BrowserThreadImpl
+    : public BrowserThread, public base::Thread {
  public:
+  // Construct a BrowserThreadImpl with the supplied identifier.  It is an error
+  // to construct a BrowserThreadImpl that already exists.
   explicit BrowserThreadImpl(BrowserThread::ID identifier);
+
+  // Special constructor for the main (UI) thread and unittests. We use a dummy
+  // thread here since the main thread already exists.
   BrowserThreadImpl(BrowserThread::ID identifier, MessageLoop* message_loop);
   virtual ~BrowserThreadImpl();
 
+ protected:
+  virtual void Init() OVERRIDE;
+  virtual void CleanUp() OVERRIDE;
+
  private:
-  // We implement most functionality on the public set of
-  // BrowserThread functions, but state is stored in the
-  // BrowserThreadImpl to keep the public API cleaner. Therefore make
-  // BrowserThread a friend class.
+  // We implement all the functionality of the public BrowserThread
+  // functions, but state is stored in the BrowserThreadImpl to keep
+  // the API cleaner. Therefore make BrowserThread a friend class.
   friend class BrowserThread;
 
   // TODO(brettw) remove this variant when Task->Closure migration is complete.
@@ -37,6 +48,13 @@ class CONTENT_EXPORT BrowserThreadImpl : public BrowserThread {
       const base::Closure& task,
       int64 delay_ms,
       bool nestable);
+
+  // Common initialization code for the constructors.
+  void Initialize();
+
+  // The identifier of this thread.  Only one thread can exist with a given
+  // identifier at a given time.
+  ID identifier_;
 };
 
 }  // namespace content