Add BlimpClientContext and factory with real and dummy implementation

blimp/client/test/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.
 
-executable("generate_localizable_strings") {
+source_set("test") {
+  testonly = true
+
   sources = [
-    "generate_localizable_strings.mm",
+    "test_blimp_client_context_delegate.cc",
+    "test_blimp_client_context_delegate.h",
   ]
+
   deps = [
     "//base",
-    "//ui/base:ui_data_pack",
+    "//blimp/client/public",
   ]
-  libs = [ "Foundation.framework" ]
 }