Make *some* version of the Win GN build work.

base/allocator/BUILD.gn

 # Copyright (c) 2013 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/allocator.gni")
 
 # Only executables and not libraries should depend on the allocator target;
 # only the application (the final executable) knows what allocator makes sense.
 # This "allocator" meta-target will forward to the default allocator according
 # to the build settings.
@@ skipping 19 matching lines @@
     script = "prep_libc.py"
     outputs = [ "$target_gen_dir/allocator/libcmt.lib" ]
     args = [
       visual_studio_path + "/vc/lib",
       rebase_path("$target_gen_dir/allocator"),
       cpu_arch,
     ]
   }
 }
 
-if (!is_android) {
+if (use_allocator == "tcmalloc") {
   # tcmalloc currently won't compile on Android.
   source_set("tcmalloc") {
     tcmalloc_dir = "//third_party/tcmalloc/chromium"
 
     sources = [
       # Generated for our configuration from tcmalloc"s build
       # and checked in.
       "$tcmalloc_dir/src/config.h",
       "$tcmalloc_dir/src/config_android.h",
       "$tcmalloc_dir/src/config_linux.h",
@@ skipping 192 matching lines @@
   visibility = [ "//base/*" ]
   sources = [
     "allocator_extension_thunks.cc",
     "allocator_extension_thunks.h",
   ]
   if (is_android && !is_debug) {
     configs -= [ "//build/config/compiler:optimize" ]
     configs += [ "//build/config/compiler:optimize_max" ]
   }
 }