Pass pref_task_runner through HttpServerPropertiesManager's cxtor so that tests could inject a Test…

net/http/http_server_properties_manager.h

Index: net/http/http_server_properties_manager.h
diff --git a/net/http/http_server_properties_manager.h b/net/http/http_server_properties_manager.h
index e1c47ff913daa3d72a5e848cc3e17f88dc215d68..e20ef59db1c16c1e221103184d6c15942037d791 100644
--- a/net/http/http_server_properties_manager.h
+++ b/net/http/http_server_properties_manager.h
@@ -40,8 +40,14 @@ class IPAddress;
 // changes are received from, and the network thread, which owns it, and it
 // persists the changes from network stack whether server supports SPDY or not.
 //
-// It must be constructed on the pref thread, to set up |pref_task_runner_| and
-// the prefs listeners.
+// There are two SingleThreadTaskRunners:
+// |pref_task_runner_| should be bound with the pref thread and is used to post
+// cache update to the pref thread;
+// |network_task_runner_| should be bound with the network thread and is used
+// to post pref update to the cache thread.
+//
+// It must be constructed with correct task runners passed in to set up
+// |pref_task_runner_| and |network_task_runner| as well as the prefs listeners.
 //
 // ShutdownOnPrefThread must be called from pref thread before destruction, to
 // release the prefs listeners on the pref thread.
@@ -81,9 +87,14 @@ class NET_EXPORT HttpServerPropertiesManager : public HttpServerProperties {
   // passed as a raw pointer rather than a scoped_refptr currently because
   // the test uses gmock and it doesn't forward move semantics properly.
   //
-  // Must be constructed on the Pref thread.
+  // There are two SingleThreadTaskRunners:
+  // |pref_task_runner| should be bound with the pref thread and is used to post
+  // cache update to the pref thread;
+  // |network_task_runner| should be bound with the network thread and is used
+  // to post pref update to the cache thread.
   HttpServerPropertiesManager(
       PrefDelegate* pref_delegate,
+      scoped_refptr<base::SingleThreadTaskRunner> pref_task_runner,
       scoped_refptr<base::SingleThreadTaskRunner> network_task_runner);
   ~HttpServerPropertiesManager() override;