[code coverage] Remove webkit layout tests sandbox for coverage.

R=stgao,liaoyuke,jbudorick

Change-Id: Ib6b8e78e90511cd5699194adba1414fbbf8985e3
Reviewed-on: https://chromium-review.googlesource.com/c/1350884Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Reviewed-by: Shuotao Gao <stgao@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Roberto Carrillo <robertocn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611253}

testing/buildbot/chromium.fyi.json

@@ -6711,6 +6711,7 @@
     "isolated_scripts": [
       {
         "args": [
+          "--additional-driver-flag=--no-sandbox",
           "--num-retries=3"
         ],
         "isolate_coverage_data": true,

testing/buildbot/test_suites.pyl

@@ -556,6 +556,7 @@
     'chromium_code_coverage_isolated_scripts': {
       'webkit_layout_tests': {
         'args': [
+          '--additional-driver-flag=--no-sandbox',
           '--num-retries=3',
         ],
         'isolate_name': 'webkit_layout_tests_exparchive',

testing/buildbot/tryserver.chromium.linux.json

@@ -683,6 +683,7 @@
     "isolated_scripts": [
       {
         "args": [
+          "--additional-driver-flag=--no-sandbox",
           "--num-retries=3"
         ],
         "isolate_coverage_data": true,