benchmarks/startup.mobile: disable on upstream bots

Currently we are investigating some noisy characteristics of the
benchmark (http://crbug.com/891797), for that we enabled systrace.

Unfortunately, on upstream bots running Android K the trace merging
fails (reasons are unknown). After the investigation is done the
systrace will be turned off anyways because it noticeably affects the
metrics (in non-representative ways).

Disabling the benchmark upstream. This. Is. Temporary. Yes.

Bug: 894744
Change-Id: I9f607e4da1e10727cd2b31b30d0ad15d53ab37c8
Reviewed-on: https://chromium-review.googlesource.com/c/1278214
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599905}

tools/perf/expectations.config

@@ -208,6 +208,10 @@ crbug.com/892223 [ Nexus_5 ] rasterize_and_record_micro.top_25/file://static_top
 crbug.com/865400 [ Nexus_5X ] rasterize_and_record_micro.top_25/file://static_top_25/yahoonews.html [ Skip ]
 crbug.com/875878 [ Nexus6_Webview ] rasterize_and_record_micro.top_25/file://static_top_25/yahoogames.html [ Skip ]
 
+# Benchmark: startup.mobile
+crbug.com/894744 [ Android ] startup.android/intent:coldish:bbc [ Skip ]
+crbug.com/894744 [ Android ] startup.android/intent:warm:bbc [ Skip ]
+
 # Benchmark: system_health.common_desktop
 crbug.com/828917 [ Mac ] system_health.common_desktop/multitab:misc:typical24 [ Skip ]
 crbug.com/874803 [ Win_10 ] system_health.common_desktop/multitab:misc:typical24 [ Skip ]