mac: Hook up allocator shim during app startup.

base/allocator/allocator_check.cc

Index: base/allocator/allocator_check.cc
diff --git a/base/allocator/allocator_check.cc b/base/allocator/allocator_check.cc
index 5a0564d2f3efd895c9e77e16ec903c7e5295e48d..f25add6862fbde6eef8fd5c2b9b58c39d6fbeb9e 100644
--- a/base/allocator/allocator_check.cc
+++ b/base/allocator/allocator_check.cc
@@ -4,6 +4,7 @@
 
 #include "base/allocator/allocator_check.h"
 
+#include "base/allocator/features.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
@@ -14,6 +15,10 @@
 #include <malloc.h>
 #endif
 
+#if defined(OS_MACOSX)
+#include "base/allocator/allocator_shim.h"
+#endif
+
 namespace base {
 namespace allocator {
 
@@ -28,6 +33,8 @@ bool IsAllocatorInitialized() {
 #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