Move session into //blimp/client/app and update GN files.

blimp/client/core/switches/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
 }
 
 source_set("switches") {
   visibility = [
-    "//blimp/client/*",
+    "//blimp/client/app:*",  # TODO(nyquist): Remove this. See crbug/651964.
+    "//blimp/client/core/*",
     "//blimp/engine:browser_tests",
   ]
 
   sources = [
     "blimp_client_switches.cc",
     "blimp_client_switches.h",
   ]
 }
 
 if (is_android) {
   android_library("switches_java") {
-    visibility = [ "//blimp/client/*" ]
+    visibility = [ "//blimp/client/core/*" ]
 
     java_files =
         [ "android/java/src/org/chromium/blimp/core/BlimpClientSwitches.java" ]
   }
 }