fix "may be used uninitialized" warnings for older compilers

content/browser/browser_thread_impl.cc

 // 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.
 
 #include "content/browser/browser_thread_impl.h"
 
 #include <string>
 
 #include "base/atomicops.h"
 #include "base/bind.h"
@@ skipping 149 matching lines @@
 NOINLINE void BrowserThreadImpl::IOThreadRun(base::MessageLoop* message_loop) {
   volatile int line_number = __LINE__;
   Thread::Run(message_loop);
   CHECK_GT(line_number, 0);
 }
 
 MSVC_POP_WARNING()
 MSVC_ENABLE_OPTIMIZE();
 
 void BrowserThreadImpl::Run(base::MessageLoop* message_loop) {
-  BrowserThread::ID thread_id;
+  BrowserThread::ID thread_id = ID_COUNT;
   if (!GetCurrentThreadIdentifier(&thread_id))
     return Thread::Run(message_loop);
 
   switch (thread_id) {
     case BrowserThread::UI:
       return UIThreadRun(message_loop);
     case BrowserThread::DB:
       return DBThreadRun(message_loop);
     case BrowserThread::FILE:
       return FileThreadRun(message_loop);
@@ skipping 60 matching lines @@
     const base::Closure& task,
     base::TimeDelta delay,
     bool nestable) {
   DCHECK(identifier >= 0 && identifier < ID_COUNT);
   // Optimization: to avoid unnecessary locks, we listed the ID enumeration in
   // order of lifetime.  So no need to lock if we know that the target thread
   // outlives current thread.
   // Note: since the array is so small, ok to loop instead of creating a map,
   // which would require a lock because std::map isn't thread safe, defeating
   // the whole purpose of this optimization.
-  BrowserThread::ID current_thread;
+  BrowserThread::ID current_thread = ID_COUNT;
   bool target_thread_outlives_current =
       GetCurrentThreadIdentifier(&current_thread) &&
       current_thread >= identifier;
 
   BrowserThreadGlobals& globals = g_globals.Get();
   if (!target_thread_outlives_current)
     globals.lock.Acquire();
 
   base::MessageLoop* message_loop =
       globals.threads[identifier] ? globals.threads[identifier]->message_loop()
@@ skipping 211 matching lines @@
   AtomicWord* storage = reinterpret_cast<AtomicWord*>(
       &globals.thread_delegates[identifier]);
   AtomicWord old_pointer = base::subtle::NoBarrier_AtomicExchange(
       storage, reinterpret_cast<AtomicWord>(delegate));
 
   // This catches registration when previously registered.
   DCHECK(!delegate || !old_pointer);
 }
 
 }  // namespace content