Use spin runloop instead of WaitForIncomingMethodCall() for test codes.

components/arc/test/fake_arc_bridge_instance.h

Index: components/arc/test/fake_arc_bridge_instance.h
diff --git a/components/arc/test/fake_arc_bridge_instance.h b/components/arc/test/fake_arc_bridge_instance.h
index 33d575175b548a126fd6eeab6cb9bb419be21445..1ebe2ac7503345d97e453d252e9002e4f84d9f28 100644
--- a/components/arc/test/fake_arc_bridge_instance.h
+++ b/components/arc/test/fake_arc_bridge_instance.h
@@ -5,6 +5,7 @@
 #ifndef COMPONENTS_ARC_TEST_FAKE_ARC_BRIDGE_INSTANCE_H_
 #define COMPONENTS_ARC_TEST_FAKE_ARC_BRIDGE_INSTANCE_H_
 
+#include "base/callback_forward.h"
 #include "base/macros.h"
 #include "components/arc/arc_bridge_service.h"
 #include "components/arc/common/arc_bridge.mojom.h"
@@ -47,6 +48,9 @@ class FakeArcBridgeInstance : public mojom::ArcBridgeInstance {
  private:
   Delegate* delegate_ = nullptr;
 
+  // Keeps quit closure to wake the running nested RunLoop.
+  base::Closure quit_closure_;
+
   // Mojo endpoints.
   mojo::Binding<mojom::ArcBridgeInstance> binding_;
   mojom::ArcBridgeHostPtr host_ptr_;