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

scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_rel_test_filter.json

Index: scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_rel_test_filter.json
diff --git a/scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_rel_test_filter.json b/scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_rel_test_filter.json
index 0e3e335710ad93788d8cd1ef28eaed60b40c610e..4d715c93bc35ad36d5760a7398adf806f9ce8d8c 100644
--- a/scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_rel_test_filter.json
+++ b/scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_rel_test_filter.json
@@ -283,7 +283,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Check",
+      "stepname:Check on Ubuntu-12.04",
       "--idempotent",
       "--user",
       "commit-bot@chromium.org",
@@ -310,7 +310,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Check",
+    "name": "[trigger] Check on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Check/Ubuntu-12.04/[dummy has/v8_linux_rel/571\", @@@",
@@ -387,7 +387,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:OptimizeForSize",
+      "stepname:OptimizeForSize on Ubuntu-12.04",
       "--idempotent",
       "--user",
       "commit-bot@chromium.org",
@@ -415,7 +415,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] OptimizeForSize",
+    "name": "[trigger] OptimizeForSize on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"OptimizeForSize/Ubuntu-12.04/[dummy has/v8_linux_rel/571\", @@@",
@@ -492,7 +492,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Test262",
+      "stepname:Test262 on Ubuntu-12.04",
       "--idempotent",
       "--user",
       "commit-bot@chromium.org",
@@ -521,7 +521,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Test262",
+    "name": "[trigger] Test262 on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Test262/Ubuntu-12.04/[dummy has/v8_linux_rel/571\", @@@",
@@ -604,7 +604,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Mjsunit - sp frame access",
+      "stepname:Mjsunit - sp frame access on Ubuntu-12.04",
       "--idempotent",
       "--user",
       "commit-bot@chromium.org",
@@ -632,7 +632,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Mjsunit - sp frame access",
+    "name": "[trigger] Mjsunit - sp frame access on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Mjsunit - sp frame access/Ubuntu-12.04/[dummy has/v8_linux_rel/571\", @@@",
@@ -709,7 +709,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Test262 - ignition",
+      "stepname:Test262 - ignition on Ubuntu-12.04",
       "--idempotent",
       "--user",
       "commit-bot@chromium.org",
@@ -739,7 +739,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Test262 - ignition",
+    "name": "[trigger] Test262 - ignition on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Test262 - ignition/Ubuntu-12.04/[dummy has/v8_linux_rel/571\", @@@",