Hookup the generic heap intercept for Windows.

build/config/allocator.gni

Index: build/config/allocator.gni
diff --git a/build/config/allocator.gni b/build/config/allocator.gni
index 10ac1adf0bd32b80a7bda79525769ed9dea2d68b..79350e5b4a7bcaf327fe4d36a4d1a004f45164bc 100644
--- a/build/config/allocator.gni
+++ b/build/config/allocator.gni
@@ -32,6 +32,12 @@ declare_args() {
 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")
+
+# NaCL doesn't obey any of this configuration.
+if (!(is_win && is_nacl)) {

[Primiano Tucci (use gerrit), 2016/07/15 14:02:10]

out of cusiosity why do you need this if?

If is_win=true and is_nacl=true, the assert will succeed both when:
use_experimental_shim = false
then
use_experimental_shim = true (by virtue of having is_win == true)

[Sigurður Ásgeirsson, 2016/07/18 19:27:07]

Yeah, this is messed up. I was under the impression that is_nacl was not
mutually exclusive to is_win. This is simply not true, however there's a wrinkle
when use_experimental_shim is set with an explicit GN argument.
In that case the flag is set both for is_nacl, and is_win, which is what
confused me.
This requires either using a different variables for the argument and modulate
it's value depending whether is_win or is_nacl, or else ignoring the flag
settings when 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")
+}
+# TODO(siggi): assert that the experimental allocator is only enabled for
+#     non-component builds on Windows.