Blimp: create MessageDispatcher class.

testing/buildbot/chromium.linux.json

 {
   "Android GN": {
     "additional_compile_targets": [
       "blimp_tests",
       "chrome_public_apk",
       "chrome_public_test_apk",
       "content_shell_apk",
       "mandoline:all"
     ],
     "gtest_tests": [
       {
+        "test": "blimp_common_unit_tests"
+      },
+      {
         "test": "html_viewer_unittests"
       },
       {
         "test": "ipc_mojo_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "mojo_common_unittests"
@@ skipping 662 matching lines @@
         "test": "aura_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "base_unittests"
       },
       {
         "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "blimp_common_unit_tests"
+      },
+      {
+        "swarming": {
           "can_use_on_swarming_builders": true,
           "shards": 5
         },
         "test": "browser_tests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "cacheinvalidation_unittests"
@@ skipping 1011 matching lines @@
       }
     ],
     "scripts": [
       {
         "name": "nacl_integration",
         "script": "nacl_integration.py"
       }
     ]
   }
 }