[Code coverage] Configure linux code coverage builder.

This change should make chromium.fyi/linux-code-coverage-generation
build one target with code coverage instrumentation and isolate it using
the chromium recipe.

This depends on change http://crrev.com/c/1258608

Tested locally:

~/chromium/src/tools$ ./mb/mb.py lookup -m chromium.fyi -b \
linux-code-coverage-generation

Writing """\
is_clang = true
is_component_build = false
is_debug = false
strip_absolute_paths_from_debug_symbols = true
symbol_level = 0
use_clang_coverage = true
use_goma = true
""" to _path_/args.gn.

R=mmoroz,stgao,liaoyuke

Bug: chromium: 891532
Change-Id: I5afdd45d149fad0f62b8a6b8f021c99d0217134c
Reviewed-on: https://chromium-review.googlesource.com/c/1255590Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Roberto Carrillo <robertocn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596514}

infra/config/global/cr-buildbucket.cfg

@@ -261,7 +261,7 @@ builder_mixins {
 builder_mixins {
   name: "code-coverage"
   recipe {
-    name: "chromium_clang_coverage_reports"
+    name: "chromium"
   }
   mixins: "fyi-ci"
   execution_timeout_secs: 72000 # 20h

testing/buildbot/chromium.fyi.json

@@ -5725,6 +5725,16 @@
       }
     ]
   },
+  "linux-code-coverage-generation": {
+    "gtest_tests": [
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "base_unittests"
+      }
+    ]
+  },
   "linux-tcmalloc-rel": {
     "gtest_tests": [
       {

testing/buildbot/test_suites.pyl

@@ -663,6 +663,10 @@
       'webapk_shell_apk_junit_tests': {},
     },
 
+    'chromium_linux_coverage_gtests': {
+      'base_unittests': {},
+    },
+
     'chromium_linux_scripts': {
       'checkdeps': {
         'script': 'checkdeps.py',

testing/buildbot/waterfalls.pyl

@@ -1365,6 +1365,11 @@
           'isolated_scripts': 'chromium_linux_rel_isolated_scripts',
         },
       },
+      'linux-code-coverage-generation': {
+        'test_suites': {
+          'gtest_tests': 'chromium_linux_coverage_gtests',
+        }
+      },
       'linux-tcmalloc-rel': {
         'test_suites': {
           'gtest_tests': 'chromium_linux_gtests',

tools/mb/mb_config.pyl

@@ -227,6 +227,7 @@
       'linux-blink-heap-incremental-marking': 'debug_bot_enable_blink_heap_incremental_marking',
       'linux-blink-heap-verification': 'release_bot_enable_blink_heap_verification_dcheck_always_on',
       'linux-chromium-tests-staging-builder': 'release_bot',
+      'linux-code-coverage-generation': 'clang_code_coverage',
       'Mac deterministic': 'release_bot_mac_strip',
       'Mac deterministic (dbg)': 'debug_bot',
 
@@ -1081,6 +1082,10 @@
       'chromeos_with_codecs', 'release_trybot', 'use_vaapi', 'no_symbols',
     ],
 
+    'clang_code_coverage': [
+      'release_bot', 'clang', 'use_clang_coverage', 'no_symbols',
+    ],
+
     'clang_release_bot_minimal_symbols_x86': [
       'clang', 'release_bot', 'minimal_symbols', 'x86',
     ],