Run blimp_unittests on Blimp engine buildbot

testing/buildbot/chromium.linux.json

 {
   "Android Arm64 Builder (dbg)": {
     "additional_compile_targets": [
       "all"
     ]
   },
   "Android Builder": {
     "additional_compile_targets": [
       "cronet_test_instrumentation_apk",
       "system_webview_apk"
@@ skipping 784 matching lines @@
       {
         "name": "webview_licenses",
         "script": "webview_licenses.py"
       }
     ]
   },
   "Blimp Linux (dbg)": {
     "gtest_tests": [
       {
         "test": "blimp_browsertests"
+      },
+      {
+        "test": "blimp_unittests"
       }
     ]
   },
   "Cast Linux": {
     "gtest_tests": [
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "base_unittests"
@@ skipping 1446 matching lines @@
         "override_compile_targets": [
           "telemetry_unittests_run"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       }
     ]
   }
 }