Hookup the generic heap intercept for Windows.

build/config/allocator.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/sanitizers/sanitizers.gni")
 
 # Temporarily disable tcmalloc on arm64 linux to get rid of compilation errors.
 if (is_android || current_cpu == "mipsel" || is_mac || is_ios || is_asan ||
     is_lsan || is_tsan || is_msan || is_win || is_syzyasan ||
     (is_linux && target_cpu == "arm64")) {
@@ skipping 14 matching lines @@
 
   # TODO(primiano): this should just become the default without having a flag,
   # but we need to get there first. http://crbug.com/550886 .
   # Causes all the allocations to be routed via allocator_shim.cc.
   use_experimental_allocator_shim = _default_use_experimental_allocator_shim
 }
 
 assert(use_allocator == "none" || use_allocator == "tcmalloc")
 
 assert(!is_win || use_allocator == "none", "Tcmalloc doesn't work on Windows.")
-assert(
-    !use_experimental_allocator_shim || is_linux || is_android,
-    "use_experimental_allocator_shim supported only on Linux and Android targets")
+
+# TODO(siggi): NaCL doesn't appear to obey this configuration, but this is still

[brettw, 2016/07/18 20:11:08]

You can do this but there's no built-in feature for this. You have to write the
code to implement the thing yourself.

If somebody sets the flag via "gn args" it will override the default set here in
all toolchains (this is how the args work). But after the declare_args block you
can always override that value again, in this case checking if we're doing a
nacl cross-compile and setting it to false.

[Sigurður Ásgeirsson, 2016/07/19 13:44:50]

I'm not sure how to do this. Adding this code:
--- cut here ---
if (is_nacl && use_experimental_allocator_shim) {
  # When the use_experimental_allocator_shim is set in GN args, it'll take
  # effect for NaCL, which doesn't obey the configuration. To reduce confusion
  # the flag is quashed to false for that case here.
  use_experimental_allocator_shim = false
}
--- cut here ---
causes GN to throw a hissy fit on me:

ERROR at //build/config/BUILD.gn:5:1: Value collision.
import("//build/config/allocator.gni")
^------------------------------------
This import contains "use_experimental_allocator_shim"
See //build/config/allocator.gni:37:37: defined here.
  use_experimental_allocator_shim = false
                                    ^----
Which would clobber the one in your current scope
See build arg file (use "gn args <out_dir>" to edit):10:35: defined here.
use_experimental_allocator_shim = true
                                  ^---
Executing import should not conflict with anything in the current
scope unless the values are identical.
See //build/config/BUILDCONFIG.gn:461:3: which caused the file to be included.
  "//build/config:feature_flags",

+#    irksome. Is there a way declare a flag which modulates the setting only
+#    under !is_nacl?
+if (!is_nacl) {
+  assert(
+      !use_experimental_allocator_shim || is_linux || is_android || is_win,
+      "use_experimental_allocator_shim supported only on Linux, Android and Windows targets")
+}
+
+if (is_win && use_experimental_allocator_shim) {
+  assert(!is_component_build,
+         "The allocator shim doesn't work for the component build on Windows.")
+}