Add msan build option.

build/standalone.gypi

Index: build/standalone.gypi
diff --git a/build/standalone.gypi b/build/standalone.gypi
index cf448f38673559de322e675b5500f8de6e1905e0..92b5ff83097991fe078a983bcd0ab22544c019a4 100644
--- a/build/standalone.gypi
+++ b/build/standalone.gypi
@@ -35,6 +35,7 @@
     'component%': 'static_library',
     'clang%': 0,
     'asan%': 0,
+    'msan%': 0,
     'visibility%': 'hidden',
     'v8_enable_backtrace%': 0,
     'v8_enable_i18n_support%': 1,
@@ -185,6 +186,22 @@
         ],
       },
     }],
+    ['msan==1', {
+      'target_defaults': {
+        'cflags_cc+': [
+          '-fno-omit-frame-pointer',
+          '-fsanitize-memory-track-origins=2',

[earthdok, 2014/07/01 12:13:22]

-fsanitize-memory-track-origins can take values from 0 (fastest, least amount of
information) to 2 (slowest, most helpful reports, experimental). Please expose
this setting rather than hardcode it to 2.

+          '-fsanitize=memory',
+          '-w',  # http://crbug.com/162783

[earthdok, 2014/07/01 12:13:22]

The linked issue refers to ASan, not MSan. We don't use -w with MSan in Chrome
and shouldn't need it for V8, either.

+        ],
+        'cflags_cc!': [
+          '-fomit-frame-pointer',
+        ],
+        'ldflags': [
+          '-fsanitize=memory',
+        ],
+      },
+    }],
     ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris" \
        or OS=="netbsd"', {
       'target_defaults': {