Make checkdeps.py check third_party.

third_party/libjingle/overrides/allocator_shim/allocator_stub.cc

 // Copyright 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.
 
-#include "allocator_shim/allocator_stub.h"
+#include "third_party/libjingle/overrides/allocator_shim/allocator_stub.h"
 
 #if defined(OS_MACOSX) || defined(OS_ANDROID)
 #error "The allocator stub isn't supported (or needed) on mac or android."
 #endif
 
 void* Allocate(std::size_t n) {
   return operator new(n);
 }
 
 void Dellocate(void* p) {
   return operator delete(p);
 }