Fix ArcBridgeBootstrap race issues.

components/arc/arc_bridge_service.h

Index: components/arc/arc_bridge_service.h
diff --git a/components/arc/arc_bridge_service.h b/components/arc/arc_bridge_service.h
index 4985cf5274bc1452559e561a1dc17b4c9f21b20d..d3ee567d7e3a58e3a202ec2b964aa83cb36372f4 100644
--- a/components/arc/arc_bridge_service.h
+++ b/components/arc/arc_bridge_service.h
@@ -5,6 +5,7 @@
 #ifndef COMPONENTS_ARC_ARC_BRIDGE_SERVICE_H_
 #define COMPONENTS_ARC_ARC_BRIDGE_SERVICE_H_
 
+#include <iosfwd>
 #include <string>
 #include <vector>
 
@@ -234,6 +235,10 @@ class ArcBridgeService {
   DISALLOW_COPY_AND_ASSIGN(ArcBridgeService);
 };
 
+// Defines "<<" operator for LOGging purpose.
+std::ostream& operator<<(
+    std::ostream& os, ArcBridgeService::StopReason reason);
+
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_ARC_BRIDGE_SERVICE_H_