Implement a ScopedThreadHeapUsage class to allow profiling per-thread heap usage.

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 f1a1e3d7ce0386361480f285cc24f206aee27ac5..53d4f1387faa0a33959a02f95ad521a34c2c4c87 100644
--- a/base/allocator/allocator_shim.h
+++ b/base/allocator/allocator_shim.h
@@ -56,12 +56,19 @@ struct AllocatorDispatch {
                           void* address,
                           size_t size);
   using FreeFn = void(const AllocatorDispatch* self, void* address);
+  // Returns the best available estimate for the actual amount of memory
+  // consumed by the allocation |address|. If possible, this should include
+  // heap overhead or at least a decent estimate of the full cost of the
+  // allocation.
+  using GetSizeEstimateFn = size_t(const AllocatorDispatch* self,

[Primiano Tucci (use gerrit), 2016/08/24 14:11:46]

I don't think that this function should be part of the shim chain. If I read the
code correctly, your intent here is not to "intercept" the GetSizeEstimate
function, you just want to provide one implementation for each OS.

I think the cleanest approach is adding a function to allocator_extensions.h,
and in the .cc file have something like
#if OS_LINUX && OS_ANDROID
 return malloc_usable_size(...)
#elif OS_WINDOWS
 whatever incantation
etc 

If you think to that, the GetEstimateSize function doesn't really depend on the
shim, you are just leveraging it here because that happens to convenientely have
the various if(OS/allocator).

[Primiano Tucci (use gerrit), 2016/08/24 15:28:46]

siggi@ and I had a chat offline. siggi@ explained me that in the near future
there is the desire to use the shim to provide some kind of
statistically-alternate-heap. In that view, makes sense for the GetSizeEstimate
function to be shimmed, as that implementation will become dependent on the
presence of the "alternate heap" shim layers.

[Sigurður Ásgeirsson, 2016/09/01 15:18:17]

Yeah - it would be nice to fully abstract the notion of a heap with the shim,
perhaps to the point of e.g. getting the aggregate memory usage for tracing
through the shim.

[Sigurður Ásgeirsson, 2016/09/01 15:18:17]

Acknowledged.

+                                   void* address);
 
   AllocFn* const alloc_function;
   AllocZeroInitializedFn* const alloc_zero_initialized_function;
   AllocAlignedFn* const alloc_aligned_function;
   ReallocFn* const realloc_function;
   FreeFn* const free_function;
+  GetSizeEstimateFn* const get_size_estimate_function;
 
   const AllocatorDispatch* next;