Ensure tests have an active task runner

content/browser/browser_thread_impl.cc

Index: content/browser/browser_thread_impl.cc
diff --git a/content/browser/browser_thread_impl.cc b/content/browser/browser_thread_impl.cc
index 78e3836dadeef038f5db6e1a7fd0b1a3352fd8b6..6a0df120d0f91abb88738ac14edbf1bfef61dfef 100644
--- a/content/browser/browser_thread_impl.cc
+++ b/content/browser/browser_thread_impl.cc
@@ -308,6 +308,9 @@ bool BrowserThreadImpl::PostTaskHelper(
     base::TimeDelta delay,
     bool nestable) {
   DCHECK(identifier >= 0 && identifier < ID_COUNT);
+  // We don't want to create a pool if none exists.
+  if (g_globals == NULL)
+    return false;
   // Optimization: to avoid unnecessary locks, we listed the ID enumeration in
   // order of lifetime.  So no need to lock if we know that the target thread
   // outlives current thread.