Bug 1323100 - Add nsThreadManager::NewNamedThread API. r=froydnj

The point of this exercise is to make the thread name available in the thread
func of the thread, so that we can register the thread with the profiler from
the very start of its lifetime, and so that registration and unregistration
can be inside the same function.

MozReview-Commit-ID: DiiMKUQVr55

xpcom/threads/nsThreadManager.cpp

@@ -248,6 +248,14 @@ NS_IMETHODIMP
 nsThreadManager::NewThread(uint32_t aCreationFlags,
                            uint32_t aStackSize,
                            nsIThread** aResult)
+{
+  return NewNamedThread(NS_LITERAL_CSTRING(""), aStackSize, aResult);
+}
+
+NS_IMETHODIMP
+nsThreadManager::NewNamedThread(const nsACString& aName,
+                                uint32_t aStackSize,
+                                nsIThread** aResult)
 {
   // Note: can be called from arbitrary threads
   
@@ -257,7 +265,7 @@ nsThreadManager::NewThread(uint32_t aCreationFlags,
   }
 
   RefPtr<nsThread> thr = new nsThread(nsThread::NOT_MAIN_THREAD, aStackSize);
-  nsresult rv = thr->Init();  // Note: blocks until the new thread has been set up
+  nsresult rv = thr->Init(aName);  // Note: blocks until the new thread has been set up
   if (NS_FAILED(rv)) {
     return rv;
   }