Blimp: create MessageDispatcher class.

blimp/BUILD.gn

 # Copyright 2015 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.
 
+# Metatarget for all of Blimp's feature code.
 group("blimp") {
   deps = [
     "//blimp/client:blimp_client",
     "//blimp/common:blimp_common",
   ]
 
   if (is_android) {
     deps += [ "//blimp/client:blimp_apk" ]
   }
 }
 
 group("blimp_tests") {
   testonly = true
 
   deps = [
     ":blimp",
   ]
 
   if (is_android) {
-    deps += [ "//blimp/client:blimp_test_apk" ]
+    deps += [
+      "//blimp/client:blimp_test_apk",
+      "//blimp/common:blimp_common_unit_tests",
+    ]
   }
 }