[libfuzzer] supporting libfuzzer on mac with asan

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 8fbd05c8b2c4720e3d6266b9329aefe33e7d17d9..f9ba3e4931ea0be9bc2e8a5991fa636d032c97d4 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -646,8 +646,6 @@ group("gn_only") {
       "//media/cast:udp_proxy",
       "//native_client/src/trusted/debug_stub:gdb_rsp_unittest",
       "//storage/browser:dump_file_system",
-      "//testing/libfuzzer/fuzzers",
-      "//testing/libfuzzer/tests:libfuzzer_tests",
       "//third_party/angle:libANGLE",
       "//third_party/angle:libEGL",
       "//third_party/angle:libGLESv2",
@@ -715,6 +713,13 @@ group("gn_only") {
     }
   }
 
+  if ((is_linux && !is_chromeos && !is_chromecast) || is_mac) {

[Alexander Potapenko, 2016/03/24 21:58:43]

Can you please add a comment about why CrOS and Chromecast aren't supported?

[aizatsky, 2016/03/24 22:31:33]

There's no particular reason. They are just not supported and they are disabled
because we don't want to spend time dealing with compilation problems/build
bots.

+    deps += [
+      "//testing/libfuzzer/fuzzers",
+      "//testing/libfuzzer/tests:libfuzzer_tests",
+    ]
+  }
+
   if (enable_nacl) {
     deps += [ "//native_client_sdk/src:nacl_core_sdk" ]
   }