Change BrowserThreadDelegate to run Init() async.

content/public/browser/browser_thread_delegate.h

Index: content/public/browser/browser_thread_delegate.h
diff --git a/content/public/browser/browser_thread_delegate.h b/content/public/browser/browser_thread_delegate.h
index f91816badce96fd504ddeccea8c56e890eea1128..ab1395ba7d123d4ca2c039003521a8f190f5f584 100644
--- a/content/public/browser/browser_thread_delegate.h
+++ b/content/public/browser/browser_thread_delegate.h
@@ -10,16 +10,15 @@ namespace content {
 // A class with this type may be registered via
 // BrowserThread::SetDelegate.
 //
-// If registered as such, it will receive an Init() call right before
-// the BrowserThread in question starts its message loop (and right
-// after the BrowserThread has done its own initialization), and a
-// CleanUp call right after the message loop ends (and before the
-// BrowserThread has done its own clean-up).
+// If registered as such, it will schedule to run Init() as the first
+// task on its message loop (after the BrowserThread has done its own
+// initialization), and receive a CleanUp call right after the message
+// loop ends (and before the BrowserThread has done its own clean-up).
 class BrowserThreadDelegate {
  public:
   virtual ~BrowserThreadDelegate() {}
 
-  // Called just prior to starting the message loop.
+  // Called as the first task on the thread's message loop.
   virtual void Init() = 0;
 
   // Called just after the message loop ends.