[Fuchsia] Grab the number of malloc'd bytes from jemalloc

runtime/vm/malloc_hooks_jemalloc.cc

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
-
-#if !defined(DART_USE_TCMALLOC) || defined(PRODUCT) ||                         \
-    defined(TARGET_ARCH_DBC) || defined(HOST_OS_FUCHSIA)
+#if defined(DART_USE_JEMALLOC) && !defined(PRODUCT) && !defined(TARGET_ARCH_DBC)

[rmacnak, 2017/04/19 22:43:59]

Not part of your change, but I don't see any reason DBC should be treated
specially.

 
 #include "vm/malloc_hooks.h"
 
+#include <jemalloc/jemalloc.h>
+
+#include "vm/json_stream.h"
+
 namespace dart {
 
 void MallocHooks::InitOnce() {
   // Do nothing.
 }
 
 
 void MallocHooks::TearDown() {
   // Do nothing.
 }
 
 
+void MallocHooks::PrintToJSONObject(JSONObject* jsobj) {
+  // Here, we ignore the value of FLAG_profiler_native_memory because we can
+  // gather this information cheaply without hooking into every call to the
+  // malloc library.
+  jsobj->AddProperty("_heapAllocatedMemoryUsage",
+                     heap_allocated_memory_in_bytes());
+  jsobj->AddProperty("_heapAllocationCount",
+                     allocation_count());
+}
+
+
+intptr_t MallocHooks::heap_allocated_memory_in_bytes() {
+  uint64_t epoch = 1;
+  size_t epoch_sz = sizeof(epoch);
+  int result = mallctl("epoch", &epoch, &epoch_sz, &epoch, epoch_sz);
+  if (result != 0) {
+    return 0;
+  }
+
+  intptr_t allocated;
+  size_t allocated_sz = sizeof(allocated);
+  result = mallctl("stats.allocated", &allocated, &allocated_sz, NULL, 0);
+  if (result != 0) {
+    return 0;
+  }
+  return allocated;
+}
+
+
+intptr_t MallocHooks::allocation_count() {
+  return 0;
+}
+
+
 bool MallocHooks::ProfilingEnabled() {
   return false;
 }
 
 
 bool MallocHooks::stack_trace_collection_enabled() {
   return false;
 }
 
 
 void MallocHooks::set_stack_trace_collection_enabled(bool enabled) {
   // Do nothing.
 }
 
 
 void MallocHooks::ResetStats() {
   // Do nothing.
 }
 
 
 bool MallocHooks::Active() {
   return false;
 }
 
 
-void MallocHooks::PrintToJSONObject(JSONObject* jsobj) {
-  // Do nothing.
-}
-
-
 Sample* MallocHooks::GetSample(const void* ptr) {
   return NULL;
 }
 
-
-intptr_t MallocHooks::allocation_count() {
-  return 0;
-}
-
-
-intptr_t MallocHooks::heap_allocated_memory_in_bytes() {
-  return 0;
-}
-
 }  // namespace dart
 
-#endif  // !defined(DART_USE_TCMALLOC) || defined(PRODUCT) ||
-        // defined(TARGET_ARCH_DBC) || defined(HOST_OS_FUCHSIA)
+#endif  // defined(DART_USE_JEMALLOC) && ...