mac: Hook up allocator shim during app startup.

base/allocator/allocator_shim.cc

Index: base/allocator/allocator_shim.cc
diff --git a/base/allocator/allocator_shim.cc b/base/allocator/allocator_shim.cc
index bad8fc6e281e2789841ae9edb6a844f9bc1df946..a680cd5f750c00a62a67a2e8a2953c5f1401a616 100644
--- a/base/allocator/allocator_shim.cc
+++ b/base/allocator/allocator_shim.cc
@@ -90,6 +90,10 @@ inline const allocator::AllocatorDispatch* GetChainHead() {
 namespace base {
 namespace allocator {
 
+#if defined(OS_MACOSX)
+bool g_is_mac_shim_layer_initialized = false;
+#endif
+
 void SetCallNewHandlerOnMallocFailure(bool value) {
   g_call_new_handler_on_malloc_failure = value;
 }
@@ -305,6 +309,8 @@ void InitializeAllocatorShim() {
   // This replaces the default malloc zone, causing calls to malloc & friends
   // from the codebase to be routed to ShimMalloc() above.
   OverrideMacSymbols();
+
+  g_is_mac_shim_layer_initialized = true;
 }
 }  // namespace allocator
 }  // namespace base