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

blimp/client/session/render_widget_feature.cc

Index: blimp/client/session/render_widget_feature.cc
diff --git a/blimp/client/session/render_widget_feature.cc b/blimp/client/session/render_widget_feature.cc
index 8a5d2945f570a6b1884904dc9bada1ff1d135e11..c75372d64ffaeff8c3662536cbad2533a880d454 100644
--- a/blimp/client/session/render_widget_feature.cc
+++ b/blimp/client/session/render_widget_feature.cc
@@ -14,6 +14,7 @@
 #include "net/base/net_errors.h"
 
 namespace blimp {
+namespace client {
 
 RenderWidgetFeature::RenderWidgetFeature() {}
 
@@ -131,4 +132,5 @@ uint32_t RenderWidgetFeature::GetRenderWidgetId(const int tab_id) {
   return 0U;
 }
 
+}  // namespace client
 }  // namespace blimp