fix "may be used uninitialized" warnings for older compilers

content/browser/browser_thread_impl.cc

Index: content/browser/browser_thread_impl.cc
diff --git a/content/browser/browser_thread_impl.cc b/content/browser/browser_thread_impl.cc
index fb6feac452fc5c276d3d98624678c37f3e0fe82c..7d8f663ddc2ecfa1d7066fa5bb3f1a705c21883b 100644
--- a/content/browser/browser_thread_impl.cc
+++ b/content/browser/browser_thread_impl.cc
@@ -167,7 +167,7 @@ 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);
 
@@ -248,7 +248,7 @@ bool BrowserThreadImpl::PostTaskHelper(
   // 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;