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

blimp/client/core/common/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")
 }
 
 if (is_android) {
   android_library("common_java") {
-    visibility = [ "//blimp/client/*" ]
+    visibility = [
+      "//blimp/client/app/*",  # TODO(nyquist): Remove this. See crbug/651964.
+      "//blimp/client/core/*",
+    ]
 
     java_files = [ "android/java/src/org/chromium/blimp/core/common/PreferencesUtil.java" ]
 
     deps = [
       "//base:base_java",
       "//blimp/client/public:public_headers_java",
     ]
   }
 }