Disabled MallocHooks code in Release due to performance concerns. Added enable_malloc_hooks flag to…

runtime/vm/flag_list.h

Index: runtime/vm/flag_list.h
diff --git a/runtime/vm/flag_list.h b/runtime/vm/flag_list.h
index 9ab1c95d386cda9f92962a382cf3c2cac4a29bef..f2ea1369f63ebc22d22daaf2a6c043330efe1ca5 100644
--- a/runtime/vm/flag_list.h
+++ b/runtime/vm/flag_list.h
@@ -25,6 +25,12 @@
 #define USING_MULTICORE false
 #endif
 
+#if defined(DEBUG)
+#define USING_DEBUG true
+#else
+#define USING_DEBUG false
+#endif
+
 // List of all flags in the VM.
 // Flags can be one of three categories:
 // * P roduct flags: Can be set in any of the deployment modes, including in
@@ -68,6 +74,10 @@
     "Dump megamorphic cache statistics")                                       \
   R(dump_symbol_stats, false, bool, false, "Dump symbol table statistics")     \
   R(enable_asserts, false, bool, false, "Enable assert statements.")           \
+  R(enable_malloc_hooks, false, bool, USING_DEBUG,                             \
+    "Enable native memory statistic collection. NOTE: This will likely result" \

[zra, 2017/02/17 23:43:27]

I'd remove the note. It's not quite *that* bad... =)

[bkonyi, 2017/02/18 00:01:11]

Well, 50% reduction in performance in some areas isn't exactly what I'd call
great :). Done.

[zra, 2017/02/18 00:03:33]

They're microbenchmarks. Not likely to be that bad in any real app.

+    " in a large performance hit when enabled. Enabled by default in Debug "   \
+    "mode")                                                                    \
   C(enable_mirrors, false, false, bool, true,                                  \
     "Disable to make importing dart:mirrors an error.")                        \
   R(enable_type_checks, false, bool, false, "Enable type checks.")             \