Reland: Lazily initialize MessageLoop for faster thread startup

base/threading/platform_thread.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // WARNING: You should *NOT* be using this class directly.  PlatformThread is
 // the low-level platform-specific abstraction to the OS's threading interface.
 // You should instead be using a message-loop driven Thread, see thread.h.
 
 #ifndef BASE_THREADING_PLATFORM_THREAD_H_
 #define BASE_THREADING_PLATFORM_THREAD_H_
@@ skipping 71 matching lines @@
       : handle_(handle),
         id_(0) {
   }
 
   PlatformThreadHandle(Handle handle,
                        PlatformThreadId id)
       : handle_(handle),
         id_(id) {
   }
 
+  PlatformThreadId id() const {
+    return id_;
+  }
+
   bool is_equal(const PlatformThreadHandle& other) const {
     return handle_ == other.handle_;
   }
 
   bool is_null() const {
     return !handle_;
   }
 
   Handle platform_handle() const {
     return handle_;
@@ skipping 93 matching lines @@
 
   static ThreadPriority GetThreadPriority(PlatformThreadHandle handle);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformThread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_PLATFORM_THREAD_H_