Cleanup blimp/client/core code organization.

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/*" ]
+
+    java_files = [ "android/java/src/org/chromium/blimp/core/common/PreferencesUtil.java" ]
+
+    deps = [
+      "//base:base_java",
+      "//blimp/client/public:public_headers_java",
+    ]
+  }
+}