Add heap allocator usage to task profiler.

base/debug/thread_heap_usage_tracker.cc

Index: base/debug/thread_heap_usage_tracker.cc
diff --git a/base/debug/thread_heap_usage_tracker.cc b/base/debug/thread_heap_usage_tracker.cc
index b9018e0c7056e2aa578e1586c462e88f58ea4008..ab8f5abf38d1068b8ee7036235ed05075b892533 100644
--- a/base/debug/thread_heap_usage_tracker.cc
+++ b/base/debug/thread_heap_usage_tracker.cc
@@ -144,7 +144,12 @@ ThreadHeapUsage* GetOrCreateThreadUsage() {
     // Prevent reentrancy due to the allocation below.
     g_thread_allocator_usage.Set(kInitializingSentinel);
 
-    allocator_usage = new ThreadHeapUsage;
+    // Delegate the allocation of the per-thread structure to the underlying
+    // heap shim, for symmetry with the deallocation. Otherwise interposing
+    // shims may mis-attribute or mis-direct this allocation.
+    const AllocatorDispatch* next = allocator_dispatch.next;

[Primiano Tucci (use gerrit), 2016/11/28 18:38:31]

add a compile_assert(std::is_pod(ThreadHeapUsage)), or this entire code is
really fragile. this works as long as the THP doesn't require a real ctor.

[Sigurður Ásgeirsson, 2016/11/30 14:41:14]

Got one of those down a couple of lines, added another one here.

+    allocator_usage = static_cast<ThreadHeapUsage*>(
+        next->alloc_function(next, sizeof(ThreadHeapUsage)));

[Primiano Tucci (use gerrit), 2016/11/28 18:38:31]

maybe a placement new is slighlty cleaner here. 
I think this needs to be a reinterpret_cast otherwise.

[Sigurður Ásgeirsson, 2016/11/30 14:41:14]

Ah, placement new - cool - haven't used it for this purpose ever. What a great
idea!

     memset(allocator_usage, 0, sizeof(*allocator_usage));
     g_thread_allocator_usage.Set(allocator_usage);
   }
@@ -159,7 +164,10 @@ ThreadHeapUsageTracker::ThreadHeapUsageTracker() : thread_usage_(nullptr) {
 }
 
 ThreadHeapUsageTracker::~ThreadHeapUsageTracker() {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  // TODO(fdoray): This DCHECK causes inexplicable fallout in Chrome. This
+  //    was isolated to a line in CalledOnValidThread reading.
+  // if (task_token_ == TaskToken::GetForCurrentThread())
+  // DCHECK(thread_checker_.CalledOnValidThread());
 
   if (thread_usage_ != nullptr) {
     // If this tracker wasn't stopped, make it inclusive so that the
@@ -254,7 +262,11 @@ ThreadHeapUsageTracker::GetDispatchForTesting() {
 void ThreadHeapUsageTracker::EnsureTLSInitialized() {
   if (!g_thread_allocator_usage.initialized()) {
     g_thread_allocator_usage.Initialize([](void* allocator_usage) {
-      delete static_cast<ThreadHeapUsage*>(allocator_usage);
+      // Delegate the freeing of the per-thread structure to the next-lower
+      // heap shim. Otherwise this free will re-initialize the TLS on thread
+      // exit.
+      allocator_dispatch.next->free_function(allocator_dispatch.next,
+                                             allocator_usage);
     });
   }
 }