Treat bisect/tryjob perf test failures as warnings.

scripts/slave/recipe_modules/auto_bisect_staging/example.expected/failed_reference_range.json

Index: scripts/slave/recipe_modules/auto_bisect_staging/example.expected/failed_reference_range.json
diff --git a/scripts/slave/recipe_modules/auto_bisect_staging/example.expected/failed_reference_range.json b/scripts/slave/recipe_modules/auto_bisect_staging/example.expected/failed_reference_range.json
index c7a0e7936243396a32c3076b83a089d435c8f382..1f939b1937b50b425cad45212a207dafecf8aaaa 100644
--- a/scripts/slave/recipe_modules/auto_bisect_staging/example.expected/failed_reference_range.json
+++ b/scripts/slave/recipe_modules/auto_bisect_staging/example.expected/failed_reference_range.json
@@ -1116,7 +1116,7 @@
       "step returned non-zero exit code: 1",
       "@@@STEP_LOG_LINE@Failure Output@benchmark text@@@",
       "@@@STEP_LOG_END@Failure Output@@@",
-      "@@@STEP_FAILURE@@@"
+      "@@@STEP_WARNINGS@@@"
     ]
   },
   {
@@ -1190,7 +1190,7 @@
       "step returned non-zero exit code: 1",
       "@@@STEP_LOG_LINE@Failure Output@benchmark text@@@",
       "@@@STEP_LOG_END@Failure Output@@@",
-      "@@@STEP_FAILURE@@@"
+      "@@@STEP_WARNINGS@@@"
     ]
   },
   {
@@ -1264,7 +1264,7 @@
       "step returned non-zero exit code: 1",
       "@@@STEP_LOG_LINE@Failure Output@benchmark text@@@",
       "@@@STEP_LOG_END@Failure Output@@@",
-      "@@@STEP_FAILURE@@@"
+      "@@@STEP_WARNINGS@@@"
     ]
   },
   {
@@ -1338,7 +1338,7 @@
       "step returned non-zero exit code: 1",
       "@@@STEP_LOG_LINE@Failure Output@benchmark text@@@",
       "@@@STEP_LOG_END@Failure Output@@@",
-      "@@@STEP_FAILURE@@@"
+      "@@@STEP_WARNINGS@@@"
     ]
   },
   {
@@ -1412,7 +1412,7 @@
       "step returned non-zero exit code: 1",
       "@@@STEP_LOG_LINE@Failure Output@benchmark text@@@",
       "@@@STEP_LOG_END@Failure Output@@@",
-      "@@@STEP_FAILURE@@@"
+      "@@@STEP_WARNINGS@@@"
     ]
   },
   {