[testing] change to use xenial for test from WebKit Linux MSAN

The builder has 20 hour hourly resource usage in p99.
http://shortn/_Guag8HYefG

So I expect this won't add much burden to existing xenial pool.
Current usage is in
https://datastudio.google.com/s/uf5Kh6NZ8XA
And we have 3400 xenial bots in MTV time now.

Test on Xenial seems generally slow, so I need to mark some tests as timeout.
https://ci.chromium.org/p/chromium/builders/ci/WebKit%20Linux%20MSAN/1075
https://ci.chromium.org/p/chromium/builders/try/linux-webkit-msan-rel/38

Total runtime: 17:00:52 (trusty) vs 19:37:25 (xenial).

Bug: 954450, 856601
Change-Id: I6ad7e33cb678e33918614c21e58dc916d6dc3e1d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1728912Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683261}

testing/buildbot/chromium.memory.json

@@ -14047,7 +14047,7 @@
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
             {
-              "os": "Ubuntu-14.04"
+              "os": "Ubuntu-16.04"
             }
           ],
           "expiration": 36000,

testing/buildbot/chromium.webkit.json

@@ -89,7 +89,7 @@
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
             {
-              "os": "Ubuntu-14.04"
+              "os": "Ubuntu-16.04"
             }
           ],
           "expiration": 36000,

testing/buildbot/test_suite_exceptions.pyl

@@ -1953,7 +1953,7 @@
         'swarming': {
           'dimension_sets': [
             {
-              'os': 'Ubuntu-14.04',
+              'os': 'Ubuntu-16.04',
             },
           ],
           'expiration': 36000,

third_party/blink/web_tests/MSANExpectations

@@ -99,7 +99,7 @@ crbug.com/851497 http/tests/devtools/tracing/timeline-style/timeline-style-recal
 
 crbug.com/862750 [ Linux ] inspector-protocol/memory/sampling-native-profile-blink-gc.js [ Pass Crash ]
 
-crbug.com/813547 [ Linux ] webaudio/BiquadFilter/tail-time-lowpass.html [ Pass Failure ]
+crbug.com/813547 [ Linux ] webaudio/BiquadFilter/tail-time-lowpass.html [ Pass Failure Timeout ]
 
 crbug.com/856601 [ Linux ] fast/css/visited-link-hang.html [ Pass Timeout ]
 crbug.com/856601 [ Linux ] http/tests/devtools/elements/styles-4/styles-inline-element-style-changes-should-not-force-style-recalc.js [ Pass Timeout ]
@@ -315,3 +315,24 @@ crbug.com/856601 [ Linux ] external/wpt/web-animations/interfaces/Animation/idlh
 
 # Sheriff 2019-07-29
 crbug.com/856601 [ Linux ] external/wpt/web-locks/idlharness.tentative.https.any.serviceworker.html [ Pass Timeout ]
+
+# Time out on MSAN
+crbug.com/856601 [ Linux ] external/wpt/IndexedDB/idlharness.any.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] external/wpt/background-fetch/idlharness.https.any.serviceworker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] external/wpt/background-fetch/idlharness.https.any.worker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] external/wpt/geolocation-API/idlharness.window.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] external/wpt/payment-handler/idlharness.https.any.worker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] external/wpt/web-nfc/idlharness.https.window.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] external/wpt/xhr/idlharness.any.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] external/wpt/xhr/idlharness.any.sharedworker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] http/tests/devtools/a11y-axe-core/settings/geolocations-a11y-test.js [ Pass Timeout ]
+crbug.com/856601 [ Linux ] virtual/not-omt-sw-fetch/external/wpt/fetch/api/idl.any.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] virtual/not-omt-sw-fetch/external/wpt/fetch/cors-rfc1918/idlharness.tentative.any.sharedworker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] virtual/not-omt-sw-fetch/external/wpt/xhr/idlharness.any.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] virtual/not-omt-sw-fetch/external/wpt/xhr/idlharness.any.sharedworker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] virtual/not-omt-sw-fetch/external/wpt/xhr/idlharness.any.worker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] virtual/omt-worker-fetch/external/wpt/fetch/cors-rfc1918/idlharness.tentative.any.sharedworker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] virtual/omt-worker-fetch/external/wpt/xhr/idlharness.any.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] virtual/omt-worker-fetch/external/wpt/xhr/idlharness.any.sharedworker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] virtual/omt-worker-fetch/external/wpt/xhr/idlharness.any.worker.html [ Pass Timeout ]
+crbug.com/856601 [ Linux ] wpt_internal/std-switch/tentative/interface.html [ Pass Timeout ]