[devtools] Filter layout tests to include only devtools relevant tests

Land only after a confirmation of successful run of devtools_frontend_linux_blink_light_rel bot.
https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/1916899

Bug: chromium:1018204
Change-Id: I42bde537652bdf445d74788fb5e6764cabe5d960
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1916466
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715663}

testing/buildbot/test_suite_exceptions.pyl

@@ -1880,6 +1880,14 @@
       'Win10 Tests x64 (dbg)',
     ],
     'modifications': {
+      'devtools_frontend_linux_blink_light_rel': {
+        'args': [
+          'http/tests/devtools',
+        ],
+        'swarming': {
+          'shards': 4,
+        },
+      },
       # chromium.fyi
       'fuchsia-fyi-x64-rel': {
         'args': [

testing/buildbot/tryserver.devtools-frontend.json

@@ -5,7 +5,8 @@
     "isolated_scripts": [
       {
         "args": [
-          "--num-retries=3"
+          "--num-retries=3",
+          "http/tests/devtools"
         ],
         "isolate_name": "blink_web_tests_exparchive",
         "merge": {
@@ -23,7 +24,7 @@
               "os": "Ubuntu-16.04"
             }
           ],
-          "shards": 12
+          "shards": 4
         }
       }
     ]

tools/mb/mb_config.pyl

@@ -955,6 +955,7 @@
 
     'tryserver.devtools-frontend': {
       # Use pure release as CI doesn't have a debug builder.
+      'devtools_frontend_linux_blink_light_rel': 'release_bot',
       'devtools_frontend_linux_blink_rel': 'release_bot',
     },