[Blimp client] Move client code into blimp::client namespace

blimp/client/session/tab_control_feature.cc

Index: blimp/client/session/tab_control_feature.cc
diff --git a/blimp/client/session/tab_control_feature.cc b/blimp/client/session/tab_control_feature.cc
index e46cbd35131a0fbcc073bedc91ffae7f42f7c176..33c45247edb4b5d6b7a7b253b291b57dee27fdc6 100644
--- a/blimp/client/session/tab_control_feature.cc
+++ b/blimp/client/session/tab_control_feature.cc
@@ -10,6 +10,7 @@
 #include "blimp/net/blimp_message_processor.h"
 
 namespace blimp {
+namespace client {
 
 TabControlFeature::TabControlFeature() {}
 
@@ -63,4 +64,5 @@ void TabControlFeature::ProcessMessage(
   NOTIMPLEMENTED();
 }
 
+}  // namespace client
 }  // namespace blimp