[tracing] Implement RealSizeEstimate for Android.

BUG=none

Review-Url: https://chromiumcodereview.appspot.com/2409703002
Cr-Commit-Position: refs/heads/master@{#426942}

base/allocator/allocator_shim_default_dispatch_to_linker_wrapped_symbols.cc

@@ -2,7 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <malloc.h>
+
 #include "base/allocator/allocator_shim.h"
+#include "build/build_config.h"
+
+#if defined(OS_ANDROID) && __ANDROID_API__ < 17
+#include <dlfcn.h>
+#endif
 
 // This translation unit defines a default dispatch for the allocator shim which
 // routes allocations to the original libc functions when using the link-time
@@ -45,7 +52,32 @@ void RealFree(const AllocatorDispatch*, void* address) {
   __real_free(address);
 }
 
-size_t RealSizeEstimate(const AllocatorDispatch*, void*) {
+#if defined(OS_ANDROID) && __ANDROID_API__ < 17
+size_t DummyMallocUsableSize(const void*) { return 0; }
+#endif
+
+size_t RealSizeEstimate(const AllocatorDispatch*, void* address) {
+#if defined(OS_ANDROID)
+#if __ANDROID_API__ < 17
+  // malloc_usable_size() is available only starting from API 17.
+  // TODO(dskiba): remove once we start building against 17+.
+  using MallocUsableSizeFunction = decltype(malloc_usable_size)*;
+  static MallocUsableSizeFunction usable_size_function = nullptr;
+  if (!usable_size_function) {
+    void* function_ptr = dlsym(RTLD_DEFAULT, "malloc_usable_size");
+    if (function_ptr) {
+      usable_size_function = reinterpret_cast<MallocUsableSizeFunction>(
+          function_ptr);
+    } else {
+      usable_size_function = &DummyMallocUsableSize;
+    }
+  }
+  return usable_size_function(address);
+#else
+  return malloc_usable_size(address);
+#endif
+#endif  // OS_ANDROID
+
   // TODO(primiano): This should be redirected to malloc_usable_size or
   //     the like.
   return 0;