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.
 
-source_set("base32") {
+source_set("test") {
+  testonly = true
+
   sources = [
-    "base32.cc",
-    "base32.h",
+    "test_blimp_client_context_delegate.cc",
+    "test_blimp_client_context_delegate.h",
   ]
 
   deps = [
     "//base",
+    "//blimp/client/public:public_headers",
   ]
 }
-
-source_set("unit_tests") {
-  testonly = true
-  sources = [
-    "base32_unittest.cc",
-  ]
-
-  deps = [
-    ":base32",
-    "//testing/gtest",
-  ]
-}