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

scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___deadcode.json

Index: scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___deadcode.json
diff --git a/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___deadcode.json b/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___deadcode.json
index 34c6813b5cb96e5ab7f2589fea6c0257335b779b..107aad9f67b4a90e174938675c73ae0588cda224 100644
--- a/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___deadcode.json
+++ b/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___deadcode.json
@@ -151,7 +151,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Check",
+      "stepname:Check on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for bot_default]",
       "--",
@@ -174,7 +174,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Check",
+    "name": "[trigger] Check on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Check/Ubuntu-12.04/[dummy has/V8 Linux - deadcode/571\", @@@",
@@ -247,7 +247,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Test262 - no variants",
+      "stepname:Test262 - no variants on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for test262]",
       "--",
@@ -272,7 +272,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Test262 - no variants",
+    "name": "[trigger] Test262 - no variants on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Test262 - no variants/Ubuntu-12.04/[dummy has/V8 Linux - deadcode/571\", @@@",
@@ -345,7 +345,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Mozilla",
+      "stepname:Mozilla on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for mozilla]",
       "--",
@@ -368,7 +368,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Mozilla",
+    "name": "[trigger] Mozilla on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Mozilla/Ubuntu-12.04/[dummy has/V8 Linux - deadcode/571\", @@@",
@@ -441,7 +441,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:SimdJs - all",
+      "stepname:SimdJs - all on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for simdjs]",
       "--",
@@ -465,7 +465,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] SimdJs - all",
+    "name": "[trigger] SimdJs - all on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"SimdJs - all/Ubuntu-12.04/[dummy has/V8 Linux - deadcode/571\", @@@",