Add tcmalloc to GN build

runtime/bin/BUILD.gn

 # Copyright (c) 2014, 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.
 
 declare_args() {
   # Whether to fall back to built-in root certificates when they cannot be
   # verified at the operating system level.
   dart_use_fallback_root_certificates = false
 
   # The BUILD.gn file that we pull from chromium as part of zlib has a
   # dependence on //base, which we don't pull in. In a standalone build of the
   # VM, we set this to //runtime/bin/zlib where we have a BUILD.gn file without
   # a dependence on //base.
   dart_zlib_path = "//third_party/zlib"
+
+  # Whether to link the standalone VM against tcmalloc. The standalone build of
+  # the VM enables this only for Linux builds.
+  dart_use_tcmalloc = false
 }
 
 resources_sources_gypi =
     exec_script("../../tools/gypi_to_gn.py",
                 [rebase_path("vmservice/vmservice_sources.gypi")],
                 "scope",
                 ["vmservice/vmservice_sources.gypi"])
 
 # Generate a resources.cc file for the service isolate without Observatory.
 action("gen_resources_cc") {
@@ skipping 484 matching lines @@
       "..:dart_maybe_product_config"
     ] + extra_configs
 
     deps = [
       ":gen_resources_cc",
       ":embedded_dart_io",
       ":libdart_builtin",
       "$dart_zlib_path",
     ] + extra_deps
 
+    if (dart_use_tcmalloc) {
+      deps += [
+        "//third_party/tcmalloc",
+      ]
+    }
+
     defines = extra_defines
 
     sources = [
       "main.cc",
       "vmservice_impl.cc",
       "vmservice_impl.h",
       "$target_gen_dir/resources_gen.cc",
     ] + extra_sources
 
     include_dirs = [
@@ skipping 129 matching lines @@
     "$dart_zlib_path",
   ]
   include_dirs = [
     "..",
     "$target_gen_dir",
   ]
   defines = [
     "TESTING",
   ]
 
+  if (dart_use_tcmalloc) {
+    deps += [
+      "//third_party/tcmalloc",
+    ]
+  }
+
   # The VM sources are already included in libdart, so we just want to add in
   # the tests here.
   vm_tests_list = exec_script("../../tools/gypi_to_gn.py",
                                 [rebase_path("../vm/vm_sources.gypi"),
                                  "--keep_only=_test.cc",
                                  "--keep_only=_test.h",],
                                 "scope",
                                 ["../vm/vm_sources.gypi"])
   vm_tests = rebase_path(vm_tests_list.sources, ".", "../vm")
 
@@ skipping 42 matching lines @@
     ]
     include_dirs = [
       "..",
     ]
     defines = [
       # The only effect of DART_SHARED_LIB is to export the Dart API.
       "DART_SHARED_LIB",
     ]
   }
 }