Blimp: create MessageDispatcher class.

blimp/BUILD.gn

Index: blimp/BUILD.gn
diff --git a/blimp/BUILD.gn b/blimp/BUILD.gn
index d3da27a91b9171ddc28ef87386da3c6171f972ba..ba9e235abc1764edb6b494023f64a48d573bf6e8 100644
--- a/blimp/BUILD.gn
+++ b/blimp/BUILD.gn
@@ -2,6 +2,7 @@
 # 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",
@@ -21,6 +22,9 @@ group("blimp_tests") {
   ]
 
   if (is_android) {
-    deps += [ "//blimp/client:blimp_test_apk" ]
+    deps += [
+      "//blimp/client:blimp_test_apk",
+      "//blimp/common:blimp_common_unit_tests",
+    ]
   }
 }