Bug 1424709 - Force disable the OSX system "nano allocator". r=spohl, a=RyanVM

We're not actually using it, and it messes up with the zone allocator in
mozjemalloc after fork(). See the lengthy analysis in
https://bugzilla.mozilla.org/show_bug.cgi?id=1424709#c34 and following.

--HG--
extra : rebase_source : b191048290a907cc7668ad7ab6369ef8661f31dc
extra : intermediate-source : 45c5d467a46077dcc3ccd59feafd0c2784432fef
extra : source : bf1efa161edb20a83fe8db2f96c51f4e66880153

browser/app/macbuild/Contents/Info.plist.in

@@ -205,6 +205,11 @@
 	<true/>
 	<key>LSApplicationCategoryType</key>
 	<string>public.app-category.productivity</string>
+	<key>LSEnvironment</key>
+	<dict>
+		<key>MallocNanoZone</key>
+		<string>0</string>
+	</dict>
 	<key>LSFileQuarantineEnabled</key>
 	<true/>
 	<key>LSMinimumSystemVersion</key>

memory/build/replace_malloc.c

@@ -513,6 +513,12 @@ register_zone(void)
    */
   malloc_zone_t *purgeable_zone = malloc_default_purgeable_zone();
 
+  // There is a problem related to the above with the system nano zone, which
+  // is hard to work around from here, and that is instead worked around by
+  // disabling the nano zone through an environment variable
+  // (MallocNanoZone=0). In Firefox, we do that through
+  // browser/app/macbuild/Contents/Info.plist.in.
+
   /* Register the custom zone.  At this point it won't be the default. */
   malloc_zone_register(&zone);