[tracing] Implement composable memory usage estimators.

base/test/BUILD.gn

Index: base/test/BUILD.gn
diff --git a/base/test/BUILD.gn b/base/test/BUILD.gn
index 788494ff6d86e148ff551ee5790511a3b77c542b..60a0550e7f6f5be59d2a2aafb82bbaf96ef9c0c7 100644
--- a/base/test/BUILD.gn
+++ b/base/test/BUILD.gn
@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/allocator.gni")
 import("//build/config/ui.gni")
 import("//build/config/nacl/config.gni")
 
@@ -75,6 +76,8 @@ static_library("test_support") {
     "scoped_feature_list.h",
     "scoped_locale.cc",
     "scoped_locale.h",
+    "scoped_memory_usage.cc",
+    "scoped_memory_usage.h",
     "scoped_path_override.cc",
     "scoped_path_override.h",
     "sequenced_task_runner_test_template.cc",
@@ -176,6 +179,13 @@ static_library("test_support") {
     ]
   }
 
+  if (!use_experimental_allocator_shim) {
+    sources -= [
+      "scoped_memory_usage.cc",
+      "scoped_memory_usage.h",
+    ]
+  }
+
   if (is_ios) {
     set_sources_assignment_filter([])
     sources += [ "test_file_util_mac.cc" ]