AppListController refactoring part 1: AppListShower implementation.

testing/buildbot/chromium.webkit.json

 {
   "WebKit Linux": {
     "gtest_tests": [
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "blink_heap_unittests"
       },
       {
@@ skipping 107 matching lines @@
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "accessibility_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
+        "test": "app_list_shower_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "app_list_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "app_shell_unittests"
       },
       {
         "swarming": {
@@ skipping 884 matching lines @@
         "name": "webkit_lint",
         "script": "webkit_lint.py"
       },
       {
         "name": "webkit_python_tests",
         "script": "webkit_python_tests.py"
       }
     ]
   }
 }