Create MSan config for Chromium recipe module + add WebRTC MSan recipe.

scripts/slave/recipe_modules/chromium/config.py

Index: scripts/slave/recipe_modules/chromium/config.py
diff --git a/scripts/slave/recipe_modules/chromium/config.py b/scripts/slave/recipe_modules/chromium/config.py
index f452a461cd170e3f944673e0d1f5c8e78572a88a..507fdc4a022916ba6bda97ea9dbc164cdfc1a2d0 100644
--- a/scripts/slave/recipe_modules/chromium/config.py
+++ b/scripts/slave/recipe_modules/chromium/config.py
@@ -333,6 +333,14 @@ def asan(c):
 def no_lsan(c):
   c.gyp_env.GYP_DEFINES['lsan'] = 0
 
+@config_ctx()
+def msan(c):
+  gyp_defs = c.gyp_env.GYP_DEFINES
+  gyp_defs['msan'] = 1
+  gyp_defs['msan_track_origins'] = 0

[earthdok, 2014/09/29 13:25:08]

msan_track_origins=0 should not be a part of the config. This option should be
chosen individually for each bot configuration as it has a significant impact on
performance. We already set a default value for it in common.gypi (currently 1).

[kjellander_chromium, 2014/09/30 10:56:40]

That makes sense, I left that variable in the existing config and used the
default for WebRTC in PS#2.

+  gyp_defs['use_instrumented_libraries'] = 1

[earthdok, 2014/09/29 13:25:08]

I'm also against adding instrumented libraries to the msan config, because
certain configurations do not need them. For example, we plan to have an MSan
bot for PDFium, which has no DSO dependencies.

Can you factor out those settings to a separate config 'instrumented_libraries',
and then apply it to the recipe using chromium_apply_config? Another benefit of
this arrangement is that it allows us to use instrumented libraries with other
sanitizers.

(Note that I don't actually know what chromium_apply_config does, just guessing
from the name.)

[kjellander_chromium, 2014/09/30 10:56:40]

Fair enough. I added it as as separate config and didn't include it in msan but
only the chromium_msan config. 

+  gyp_defs['instrumented_libraries_jobs'] = 10
+
 @config_ctx(group='memory_tool')
 def memcheck(c):
   _memory_tool(c, 'memcheck')
@@ -400,6 +408,10 @@ def chromium_asan(c):
   c.runtests.test_args.append('--test-launcher-batch-limit=1')
   c.runtests.test_args.append('--test-launcher-print-test-stdio=always')
 
+@config_ctx(includes=['ninja', 'clang', 'goma', 'msan'])
+def chromium_msan(c):
+  c.compile_py.default_targets = ['All', 'chromium_builder_tests']
+
 @config_ctx(includes=['ninja', 'clang', 'goma', 'syzyasan'])
 def chromium_syzyasan(c):
   c.compile_py.default_targets = ['All', 'chromium_builder_tests']