Add minimal LLVM sanity coverage (sancov) reporting for unittests.

webrtc/build/common.gypi

 # Copyright (c) 2012 The WebRTC 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 in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 # This file contains common settings for building WebRTC components.
 
@@ skipping 80 matching lines @@
     # third party code will still have the reduced warning settings.
     'chromium_code': 1,
 
     # Targets are by default not NaCl untrusted code. Use this variable exclude
     # code that uses libraries that aren't available in the NaCl sandbox.
     'nacl_untrusted_build%': 0,
 
     # Set to 1 to enable code coverage on Linux using the gcov library.
     'coverage%': 0,
 
+    # Set to "func", "block", "edge" for coverage generation.
+    # At unit test runtime set UBSAN_OPTIONS="coverage=1".
+    # It is recommend to set include_examples=0.
+    # Use llvm's sancov -html-report for human readable reports.
+    # See http://clang.llvm.org/docs/SanitizerCoverage.html .
+    'webrtc_sanitize_coverage%': "",

[phoglund, 2016/07/19 19:12:40]

We need to have parity between gn and gyp; please add this variable to
build/webrtc.gni, and the flag fiddling to webrtc/BUILD.gn (in
common_inherited_config). Ensure it works with for instance

gn gen out/Default --args="webrtc_sanitize_coverage=func"
ninja -C out/Default some_target

[johan, 2016/07/21 12:33:22]

Done, gn files use name pattern "rtc_.*" while gyp files use 'webrtc_.*' for
arguments.
gn gen out/Default --args='rtc_sanitize_coverage="func"'

+
     # Remote bitrate estimator logging/plotting.
     'enable_bwe_test_logging%': 0,
 
     # Selects fixed-point code where possible.
     'prefer_fixed_point%': 0,
 
     # Enable data logging. Produces text files with data logged within engines
     # which can be easily parsed for offline processing.
     'enable_data_logging%': 0,
 
@@ skipping 286 matching lines @@
             ],
           }],
         ],
       }],
       ['coverage==1 and OS=="linux"', {
         'cflags': [ '-ftest-coverage',
                     '-fprofile-arcs' ],
         'ldflags': [ '--coverage' ],
         'link_settings': { 'libraries': [ '-lgcov' ] },
       }],
+     ['webrtc_sanitize_coverage!=""', {
+        'cflags': [ '-fsanitize-coverage=<(webrtc_sanitize_coverage)' ],
+        'ldflags': [ '-fsanitize-coverage=<(webrtc_sanitize_coverage)' ],
+     }],
+     ['webrtc_sanitize_coverage!="" and OS=="mac"', {
+        'xcode_settings': {
+            'OTHER_CFLAGS': [
+               '-fsanitize-coverage=func',
+            ],
+         },
+      }],
       ['os_posix==1', {
         # For access to standard POSIXish features, use WEBRTC_POSIX instead of
         # a more specific macro.
         'defines': [
           'WEBRTC_POSIX',
         ],
       }],
       ['OS=="ios"', {
         'defines': [
           'WEBRTC_MAC',
@@ skipping 168 matching lines @@
         }],
         ['OS=="freebsd"', {
           'defines': [
             'FREEBSD',
           ],
         }],
       ],
     },
   }, # target_defaults
 }