Only run mojo_{shell,application_manager,view_manager}_unittests on linux

BUG=
R=sky@chromium.org

Review URL: https://codereview.chromium.org/589493003

Cr-Commit-Position: refs/heads/master@{#295778}

testing/buildbot/chromium.win.json

@@ -110,10 +110,7 @@
       "mojo_public_environment_unittests",
       "mojo_public_system_unittests",
       "mojo_public_utility_unittests",
-      "mojo_application_manager_unittests",
-      "mojo_shell_tests",
       "mojo_system_unittests",
-      "mojo_view_manager_unittests",
       "sync_unit_tests",
       "unit_tests",
       "sql_unittests",
@@ -179,10 +176,7 @@
       "mojo_public_environment_unittests",
       "mojo_public_system_unittests",
       "mojo_public_utility_unittests",
-      "mojo_application_manager_unittests",
-      "mojo_shell_tests",
       "mojo_system_unittests",
-      "mojo_view_manager_unittests",
       "sync_unit_tests",
       "unit_tests",
       "sql_unittests",
@@ -245,10 +239,7 @@
       "mojo_public_environment_unittests",
       "mojo_public_system_unittests",
       "mojo_public_utility_unittests",
-      "mojo_application_manager_unittests",
-      "mojo_shell_tests",
       "mojo_system_unittests",
-      "mojo_view_manager_unittests",
       "sync_unit_tests",
       "unit_tests",
       "sql_unittests",
@@ -315,10 +306,7 @@
       "mojo_public_environment_unittests",
       "mojo_public_system_unittests",
       "mojo_public_utility_unittests",
-      "mojo_application_manager_unittests",
-      "mojo_shell_tests",
       "mojo_system_unittests",
-      "mojo_view_manager_unittests",
       {"test": "browser_tests", "shard_index": 2, "total_shards": 5}
     ]
   },

testing/buildbot/chromium_trybot.json

@@ -98,8 +98,14 @@
     "mojo_public_environment_unittests",
     "mojo_public_system_unittests",
     "mojo_public_utility_unittests",
-    "mojo_application_manager_unittests",
-    "mojo_shell_tests",
+    {
+      "test": "mojo_application_manager_unittests",
+      "platforms": ["linux"]
+    },
+    {
+      "test": "mojo_shell_tests",
+      "platforms": ["linux"]
+    },
     "mojo_system_unittests",
     {
       "test": "nacl_loader_unittests",
@@ -166,7 +172,7 @@
     },
     {
       "test": "mojo_view_manager_unittests",
-      "platforms": ["linux", "win"]
+      "platforms": ["linux"]
     },
     {
       "test": "views_unittests",