Re-fix http://crbug.com/87176, and add a test.

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 56d8549a41cd985ee3057693b9864415522704e1..27d5e4cdbfc1e71e26885d927ae0035464e01f14 100644
--- a/content/browser/browser_main_loop.cc
+++ b/content/browser/browser_main_loop.cc
@@ -265,7 +265,9 @@ class BrowserMainLoop::MemoryObserver : public base::MessageLoop::TaskObserver {
 
 // static
 media::AudioManager* BrowserMainLoop::GetAudioManager() {
-  return g_current_browser_main_loop->audio_manager_.get();
+  if (g_current_browser_main_loop)
+    return g_current_browser_main_loop->audio_manager_.get();
+  return NULL;
 }
 
 // static
@@ -275,7 +277,9 @@ AudioMirroringManager* BrowserMainLoop::GetAudioMirroringManager() {
 
 // static
 MediaStreamManager* BrowserMainLoop::GetMediaStreamManager() {
-  return g_current_browser_main_loop->media_stream_manager_.get();
+  if (g_current_browser_main_loop)
+    return g_current_browser_main_loop->media_stream_manager_.get();
+  return NULL;
 }
 // BrowserMainLoop construction / destruction =============================