swarming: always append task's OS dimension to step name

scripts/slave/recipes/chromium.expected/full_client_skia_Linux_Tests.json

Index: scripts/slave/recipes/chromium.expected/full_client_skia_Linux_Tests.json
diff --git a/scripts/slave/recipes/chromium.expected/full_client_skia_Linux_Tests.json b/scripts/slave/recipes/chromium.expected/full_client_skia_Linux_Tests.json
index 6e874ebb5b85617e58927038b5ceb789fcd6adf5..156e8f19bf6439c4a26aa24496cfc44e24388edf 100644
--- a/scripts/slave/recipes/chromium.expected/full_client_skia_Linux_Tests.json
+++ b/scripts/slave/recipes/chromium.expected/full_client_skia_Linux_Tests.json
@@ -309,14 +309,14 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:browser_tests",
+      "stepname:browser_tests on Ubuntu-12.04",
       "--idempotent",
       "ffffffffffffffffffffffffffffffffffffffff",
       "--",
       "--test-launcher-summary-output=${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] browser_tests",
+    "name": "[trigger] browser_tests on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"browser_tests/Ubuntu-12.04/ffffffffff/Linux Tests/571\", @@@",
@@ -355,7 +355,7 @@
       "browser_tests/Ubuntu-12.04/ffffffffff/Linux Tests/571"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "browser_tests",
+    "name": "browser_tests on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LINK@shard #0 isolated out@blah@@@"
     ]
@@ -374,14 +374,14 @@
       "--build-number",
       "571",
       "--test-type",
-      "browser_tests",
+      "browser_tests on Ubuntu-12.04",
       "--test-results-server",
       "test-results.appspot.com",
       "--chrome-revision",
       "143121"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "Upload to test-results [browser_tests]"
+    "name": "Upload to test-results [browser_tests on Ubuntu-12.04]"
   },
   {
     "name": "$result",