Use individual functions to join browser threads.

content/browser/browser_main_loop.cc

Index: content/browser/browser_main_loop.cc
diff --git a/content/browser/browser_main_loop.cc b/content/browser/browser_main_loop.cc
index c5c50741838b03d2225f44d1dc340c610702d674..12d829dee7d349634bfcb0e7bfe47369bb86f271 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -239,6 +239,45 @@ bool ShouldInitializeBrowserGpuChannelAndTransportSurface() {
 }
 #endif
 
+// Disable optimizations for this block of functions so the compiler doesn't
+// merge them all together. This makes it possible to tell what thread was
+// unresponsive by inspecting the callstack.
+MSVC_DISABLE_OPTIMIZE()
+MSVC_PUSH_DISABLE_WARNING(4748)
+
+NOINLINE void ResetThread_DB(scoped_ptr<BrowserProcessSubThread> thread) {
+  thread.reset();
+}
+
+NOINLINE void ResetThread_FILE(scoped_ptr<BrowserProcessSubThread> thread) {
+  thread.reset();
+}
+
+NOINLINE void ResetThread_FILE_USER_BLOCKING(
+    scoped_ptr<BrowserProcessSubThread> thread) {
+  thread.reset();
+}
+
+NOINLINE void ResetThread_PROCESS_LAUNCHER(
+    scoped_ptr<BrowserProcessSubThread> thread) {
+  thread.reset();
+}
+
+NOINLINE void ResetThread_CACHE(scoped_ptr<BrowserProcessSubThread> thread) {
+  thread.reset();
+}
+
+NOINLINE void ResetThread_IO(scoped_ptr<BrowserProcessSubThread> thread) {
+  thread.reset();
+}
+
+NOINLINE void ResetThread_IndexedDb(scoped_ptr<base::Thread> thread) {
+  thread.reset();
+}
+
+MSVC_POP_WARNING()
+MSVC_ENABLE_OPTIMIZE();
+
 }  // namespace
 
 // The currently-running BrowserMainLoop.  There can be one or zero.
@@ -808,13 +847,7 @@ void BrowserMainLoop::ShutdownThreadsAndCleanUp() {
     switch (thread_id) {
       case BrowserThread::DB: {
           TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:DBThread");

[sky, 2014/08/15 04:48:01]

nit: spacing is off in all these case statements, should be 2 space indented (as
line 888).

[rvargas (doing something else), 2014/08/15 18:01:26]

Done.

-          db_thread_.reset();
-        }
-        break;
-      case BrowserThread::FILE_USER_BLOCKING: {
-          TRACE_EVENT0("shutdown",
-                       "BrowserMainLoop::Subsystem:FileUserBlockingThread");
-          file_user_blocking_thread_.reset();
+          ResetThread_DB(db_thread_.Pass());
         }
         break;
       case BrowserThread::FILE: {
@@ -825,22 +858,28 @@ void BrowserMainLoop::ShutdownThreadsAndCleanUp() {
           if (resource_dispatcher_host_)
             resource_dispatcher_host_.get()->save_file_manager()->Shutdown();
 #endif  // !defined(OS_IOS)
-          file_thread_.reset();
+          ResetThread_FILE(file_thread_.Pass());
+        }
+        break;
+      case BrowserThread::FILE_USER_BLOCKING: {
+          TRACE_EVENT0("shutdown",
+                       "BrowserMainLoop::Subsystem:FileUserBlockingThread");
+          ResetThread_FILE_USER_BLOCKING(file_user_blocking_thread_.Pass());
         }
         break;
       case BrowserThread::PROCESS_LAUNCHER: {
           TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:LauncherThread");
-          process_launcher_thread_.reset();
+          ResetThread_PROCESS_LAUNCHER(process_launcher_thread_.Pass());
         }
         break;
       case BrowserThread::CACHE: {
           TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:CacheThread");
-          cache_thread_.reset();
+          ResetThread_CACHE(cache_thread_.Pass());
         }
         break;
       case BrowserThread::IO: {
           TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:IOThread");
-          io_thread_.reset();
+          ResetThread_IO(io_thread_.Pass());
         }
         break;
       case BrowserThread::UI:
@@ -854,7 +893,7 @@ void BrowserMainLoop::ShutdownThreadsAndCleanUp() {
 #if !defined(OS_IOS)
   {
     TRACE_EVENT0("shutdown", "BrowserMainLoop::Subsystem:IndexedDBThread");
-    indexed_db_thread_.reset();
+    ResetThread_IndexedDb(indexed_db_thread_.Pass());
   }
 #endif