[coverage] Filter some files from instrumentation.

build/coverage_wrapper.py

Index: build/coverage_wrapper.py
diff --git a/build/coverage_wrapper.py b/build/coverage_wrapper.py
new file mode 100755
index 0000000000000000000000000000000000000000..c1db754c94c1b4c323bda1551f482d007dc0fb50
--- /dev/null
+++ b/build/coverage_wrapper.py
@@ -0,0 +1,28 @@
+#!/usr/bin/env python
+# Copyright 2016 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# CC/CXX wrapper script that excludes certain file patterns from coverage
+# instrumentation.
+
+import re
+import subprocess
+import sys
+
+exclusions = [
+  'src/third_party',
+  'third_party',
+  'test',
+  'testing',
+]
+
+args = sys.argv[1:]
+text = ' '.join(sys.argv[2:])
+for exclusion in exclusions:
+  if re.search(r'\-o obj/%s[^ ]*\.o' % exclusion, text):
+    args.remove('-fprofile-arcs')
+    args.remove('-ftest-coverage')
+    break
+
+sys.exit(subprocess.check_call(args))