Update Java Bridge to use its own thread in the browser process

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 1e0808c6cf2e4dd96051644d77b0044c23c6b02e..290cca61b0c248c2f1ec1ebc4ec7ab56930286b9 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -343,6 +343,11 @@ void BrowserMainLoop::RunMainMessageLoopParts(
         thread_to_start = &cache_thread_;
         options = &io_message_loop_options;
         break;
+      case BrowserThread::JAVA_BRIDGE:
+#if defined(ENABLE_JAVA_BRIDGE)
+        thread_to_start = &java_bridge_thread_;
+#endif
+        break;
       case BrowserThread::IO:
         thread_to_start = &io_thread_;
         options = &io_message_loop_options;
@@ -371,8 +376,6 @@ void BrowserMainLoop::RunMainMessageLoopParts(
     } else if (thread_to_start) {
       (*thread_to_start).reset(new BrowserProcessSubThread(id));
       (*thread_to_start)->StartWithOptions(*options);
-    } else {
-      NOTREACHED();
     }
 
     if (parts_.get())
@@ -429,6 +432,12 @@ void BrowserMainLoop::ShutdownThreadsAndCleanUp() {
     //
     // - (Not sure why the WEB_SOCKET_PROXY thread is stopped first.)
     //
+    // - The JAVA_BRIDGE thread receives messages from the UI thread, and posts
+    //   messages to and receives messages from the IO thread. Of the
+    //   interactions with the IO thread, receiving messages is more common, so
+    //   make sure this thread outlives the IO thread to take advantage of the
+    //   optimization in BrowserThread.
+    //
     // - The IO thread is the only user of the CACHE thread.
     //
     // - The PROCESS_LAUNCHER thread must be stopped after IO in case
@@ -463,6 +472,11 @@ void BrowserMainLoop::ShutdownThreadsAndCleanUp() {
       case BrowserThread::CACHE:
         thread_to_stop = &cache_thread_;
         break;
+      case BrowserThread::JAVA_BRIDGE:
+#if defined(ENABLE_JAVA_BRIDGE)
+        thread_to_stop = &java_bridge_thread_;
+#endif
+        break;
       case BrowserThread::IO:
         thread_to_stop = &io_thread_;
         break;
@@ -487,8 +501,6 @@ void BrowserMainLoop::ShutdownThreadsAndCleanUp() {
       webkit_thread_.reset();
     } else if (thread_to_stop) {
       thread_to_stop->reset();
-    } else {
-      NOTREACHED();
     }
 
     if (parts_.get())