metrics: Connect leak detector to allocator

base/allocator/allocator_extension.h

Index: base/allocator/allocator_extension.h
diff --git a/base/allocator/allocator_extension.h b/base/allocator/allocator_extension.h
index 64bfd1cc4acaa3fe2a8fc1e8f80ab1fe674f3856..f19d7b557b16c603da61227dfb69f48d95fa69fd 100644
--- a/base/allocator/allocator_extension.h
+++ b/base/allocator/allocator_extension.h
@@ -7,12 +7,18 @@
 
 #include <stddef.h> // for size_t
 
+#include <type_traits>  // for std::add_pointer
+
 #include "base/base_export.h"
 #include "build/build_config.h"
 
 namespace base {
 namespace allocator {
 
+// Callback types for alloc and free.
+using AllocHookFunc = std::add_pointer<void(const void*, size_t)>::type;

[Primiano Tucci (use gerrit), 2016/03/02 22:16:11]

I think there is an unresolved comment here, maybe it just got lost in the
thread:

copy-pasting:
std::add_pointer<void(const void*, size_t)>::type;
What is the benefit of std::add_pointer as opposite to just a function pointer
(see below). I don't see any precedence in the codebase nor it seems whitelisted
in https://chromium-cpp.appspot.com/.

e.g. using AllocHookFunc = void (*)(const void*, size_t);

[Simon Que, 2016/03/02 22:35:25]

Done.

+using FreeHookFunc = std::add_pointer<void(const void*)>::type;
+
 // Request that the allocator release any free memory it knows about to the
 // system.
 BASE_EXPORT void ReleaseFreeMemory();
@@ -25,6 +31,25 @@ BASE_EXPORT bool GetNumericProperty(const char* name, size_t* value);
 
 BASE_EXPORT bool IsHeapProfilerRunning();
 
+// Register callbacks for alloc and free. Can only store one callback at a time
+// for each of alloc and free.
+BASE_EXPORT void SetHooks(AllocHookFunc alloc_hook, FreeHookFunc free_hook);
+
+// Attempts to unwind the call stack from the current location where this
+// function is being called from. Must be called from a hook function registered
+// by calling SetSingle{Alloc,Free}Hook, directly or indirectly.
+//
+// Arguments:
+//   stack:          pointer to a pre-allocated array of void*'s.
+//   max_stack_size: indicates the size of the array in |stack|.
+//   skip_count:     Indicates how many initial call stack levels to skip before
+//                   storing the caller of alloc/free. This value might not be
+//                   used, depending on the specific implementation.
+//
+// Returns the number of call stack frames stored in |stack|, or 0 if no call
+// stack information is available.
+BASE_EXPORT int GetCallStack(void** stack, int max_stack_size, int skip_count);

[Primiano Tucci (use gerrit), 2016/03/02 22:16:11]

There is another unresolved comment here:
It looks like this is really not used in the .cc file. What's the point of
adding a dead parameter?

[Simon Que, 2016/03/02 22:35:25]

Done.

+
 }  // namespace allocator
 }  // namespace base