Hook up allocator shim on mac.

base/allocator/allocator_shim.h

Index: base/allocator/allocator_shim.h
diff --git a/base/allocator/allocator_shim.h b/base/allocator/allocator_shim.h
index 8fd060fca6aaeee76a74cdd613af09579a56b77d..2595b1fce09a74ef9da152e43f08aa5ae1ec71d4 100644
--- a/base/allocator/allocator_shim.h
+++ b/base/allocator/allocator_shim.h
@@ -8,6 +8,7 @@
 #include <stddef.h>
 
 #include "base/base_export.h"
+#include "build/build_config.h"
 
 namespace base {
 namespace allocator {
@@ -62,6 +63,13 @@ struct AllocatorDispatch {
   // allocation. If no good estimate is possible, returns zero.
   using GetSizeEstimateFn = size_t(const AllocatorDispatch* self,
                                    void* address);
+  using BatchMallocFn = unsigned(const AllocatorDispatch* self,
+                                 size_t size,
+                                 void** results,
+                                 unsigned num_requested);
+  using BatchFreeFn = void(const AllocatorDispatch* self,
+                           void** to_be_freed,
+                           unsigned num_to_be_freed);
 
   AllocFn* const alloc_function;
   AllocZeroInitializedFn* const alloc_zero_initialized_function;
@@ -69,6 +77,8 @@ struct AllocatorDispatch {
   ReallocFn* const realloc_function;
   FreeFn* const free_function;
   GetSizeEstimateFn* const get_size_estimate_function;
+  BatchMallocFn* const batch_malloc_function;
+  BatchFreeFn* const batch_free_function;
 
   const AllocatorDispatch* next;
 
@@ -97,6 +107,11 @@ BASE_EXPORT void InsertAllocatorDispatch(AllocatorDispatch* dispatch);
 // in malloc(), which we really don't want.
 BASE_EXPORT void RemoveAllocatorDispatchForTesting(AllocatorDispatch* dispatch);
 
+#if defined(OS_MACOSX)

[Primiano Tucci (use gerrit), 2017/01/28 05:10:02]

Was this the argument of the discussion with dskiba?
Honestly I like the #ifdef here, as it will make explicit in content_main (or
wherever this will be called) that this happens only on OSX.

[erikchen, 2017/01/31 02:21:22]

No, the discussion was about whether the members batch_malloc_function,
batch_free_function, and free_definite_size_function should be if-defed. 

+// On macOS, the allocator shim needs to be turned on during runtime.
+BASE_EXPORT void InitializeAllocatorShim();
+#endif  // defined(OS_MACOSX)
+
 }  // namespace allocator
 }  // namespace base