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

scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux64___debug___greedy_allocator_bisect_tester.json

Index: scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux64___debug___greedy_allocator_bisect_tester.json
diff --git a/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux64___debug___greedy_allocator_bisect_tester.json b/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux64___debug___greedy_allocator_bisect_tester.json
index 33d5cff53d1c09a6d8fafed2f7af7cdb5290694b..08b1558e222757a57ce2585548fd77084e30604f 100644
--- a/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux64___debug___greedy_allocator_bisect_tester.json
+++ b/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux64___debug___greedy_allocator_bisect_tester.json
@@ -151,7 +151,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Check",
+      "stepname:Check on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for bot_default]",
       "--",
@@ -175,7 +175,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Check",
+    "name": "[trigger] Check on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Check/Ubuntu-12.04/[dummy has/V8 Linux64 - debug - greedy allocator/571\", @@@",
@@ -248,7 +248,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Benchmarks",
+      "stepname:Benchmarks on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for benchmarks]",
       "--",
@@ -273,7 +273,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Benchmarks",
+    "name": "[trigger] Benchmarks on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Benchmarks/Ubuntu-12.04/[dummy has/V8 Linux64 - debug - greedy allocator/571\", @@@",
@@ -346,7 +346,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:SimdJs - all",
+      "stepname:SimdJs - all on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for simdjs]",
       "--",
@@ -371,7 +371,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] SimdJs - all",
+    "name": "[trigger] SimdJs - all on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"SimdJs - all/Ubuntu-12.04/[dummy has/V8 Linux64 - debug - greedy allocator/571\", @@@",
@@ -742,7 +742,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Retry",
+      "stepname:Retry on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for bisection]",
       "--",
@@ -769,7 +769,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "Bisect a0.[trigger] Retry",
+    "name": "Bisect a0.[trigger] Retry on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ -921,7 +921,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Retry",
+      "stepname:Retry on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for bisection]",
       "--",
@@ -948,7 +948,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "Bisect a1.[trigger] Retry",
+    "name": "Bisect a1.[trigger] Retry on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",