Allocator shim skeleton + Linux impl behind a build flag

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")
 
 if (is_android || current_cpu == "mipsel" || is_mac || is_ios || is_asan ||
     is_lsan || is_tsan || is_msan || is_win || is_syzyasan) {
   _default_allocator = "none"
 } else {
   _default_allocator = "tcmalloc"
 }
 
 declare_args() {
   # Memory allocator to use. Set to "none" to use default allocator.
   use_allocator = _default_allocator
 
   # 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 = false
 }
 
 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,
+assert(!use_experimental_allocator_shim || is_linux || is_nacl,

[Nico, 2016/03/08 03:08:42]

why is this needed?

[Primiano Tucci (use gerrit), 2016/03/08 20:54:05]

Oh that didn't really work as expected, removing it.

The full story is that nacl is special in ways I often don't understand.
My plan for flipping the flag in the next CL, is to enable only for non-nacl as
I don't see a compelling use case to have the shim on nacl (unless I am missing
something).

What I get when building with nacl and the shim is:
../../base/allocator/allocator_shim_override_cpp_symbols.h:20:25: error:
function previously declared with an explicit exception specification redeclared
with an implicit exception specification
[-Werror,-Wimplicit-exception-spec-mismatch]
SHIM_ALWAYS_EXPORT void operator delete(void* p) __THROW
                        ^
/s/chrome-shim/src/native_client/toolchain/linux_x86/pnacl_newlib/le32-nacl/include/c++/v1/new:133:30:
note: previous declaration is here
_LIBCPP_NEW_DELETE_VIS void  operator delete(void* __p) _NOEXCEPT;
                             ^

So that thing was really a note-to-self to rule out nacl from the flag. But it
seems that I get if I forget that error is enough of a reminder.

        "use_experimental_allocator_shim supported only on Linux")