[code coverage] Hard code the path of the coverage wrapper input file.

R=jbudorick,stgao,liaoyuke

Change-Id: I5ce2f9c8aa14fe5114220ee2438ea48acec4f8a1
Reviewed-on: https://chromium-review.googlesource.com/c/1327165
Commit-Queue: Roberto Carrillo <robertocn@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606754}

.gitignore

@@ -33,6 +33,7 @@
 .*.sw?
 .DS_Store
 .cipd
+.clang-coverage
 .classpath
 .cproject
 .gdb_history

tools/mb/mb_config.pyl

@@ -1093,6 +1093,7 @@
 
     'clang_code_coverage_trybot': [
       'gpu_tests', 'use_dummy_lastchange', 'release_trybot', 'clang', 'use_clang_coverage', 'no_symbols',
+      'partial_clang_instrumentation'
     ],
 
     'clang_release_bot_minimal_symbols_x86': [
@@ -2062,6 +2063,15 @@
       'gn_args': 'ozone_platform_headless=true',
     },
 
+    # Used to pass the list of files to instrument for coverage to the compile
+    # wrapper. See:
+    # https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/clang_coverage/api.py
+    # and
+    # https://cs.chromium.org/chromium/src/docs/clang_code_coverage_wrapper.md
+    'partial_clang_instrumentation': {
+      'gn_args': 'coverage_instrumentation_input_file="//.clang-coverage/files_to_instrument.txt"'
+    },
+
     'pdf_xfa': {
       'gn_args': 'pdf_enable_xfa=true',
     },