mac: Hook up allocator shim during app startup.

base/allocator/allocator_check.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/allocator/allocator_check.h"
 
+#include "base/allocator/features.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
 #include "base/allocator/allocator_shim_win.h"
 #endif
 
 #if defined(OS_LINUX)
 #include <malloc.h>
 #endif
 
+#if defined(OS_MACOSX)
+#include "base/allocator/allocator_shim.h"
+#endif
+
 namespace base {
 namespace allocator {
 
 bool IsAllocatorInitialized() {
 #if defined(OS_WIN) && defined(ALLOCATOR_SHIM)
   // Set by allocator_shim_win.cc when the shimmed _set_new_mode() is called.
   return g_is_win_shim_layer_initialized;
 #elif defined(OS_LINUX) && defined(USE_TCMALLOC) && \
     !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
 // From third_party/tcmalloc/chromium/src/gperftools/tcmalloc.h.
 // TODO(primiano): replace with an include once base can depend on allocator.
 #define TC_MALLOPT_IS_OVERRIDDEN_BY_TCMALLOC 0xbeef42
   return (mallopt(TC_MALLOPT_IS_OVERRIDDEN_BY_TCMALLOC, 0) ==
           TC_MALLOPT_IS_OVERRIDDEN_BY_TCMALLOC);
+#elif defined(OS_MACOSX) && BUILDFLAG(USE_EXPERIMENTAL_ALLOCATOR_SHIM)

[Primiano Tucci (use gerrit), 2017/02/07 11:58:08]

I think this should really be:
#elif defined(OS_MACOSX) && !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
return base::allocator::g_replaced_default_zone  // (from
allocator_interception_mac.mm)
#endif

note how I voluntarily omitted USE_EXPERIMENTAL_ALLOCATOR_SHIM.

Rationale?
This function really checks that the allocator hooks are armed, so that the
suicide on OOM will work if enabled via EnabledTerminationOnOOM.
On OSX there are two ways to achieve this:
1) current state, without the shim: InterceptAllocationsMac replaces all the
zones including the default one (InterceptAllocationsMac() ->
ReplaceFunctionsForDefaultZone())
2) future state, with the shime: the shim layer will use
StoreFunctionsForDefaultZone to setup itself (InitializeAllocatorShim() ->
OverrideMacSymbols() -> ReplaceFunctionsForDefaultZone)

[erikchen, 2017/02/09 23:49:04]

Done.
Thanks for the explanation. This wasn't clear from the name of the function, and
there is no documentation. I didn't realize this was supposed to return true
iff. suicide on OOM works correctly.

+  return g_is_mac_shim_layer_initialized;
 #else
   return true;
 #endif
 }
 
 }  // namespace allocator
 }  // namespace base