Fixing remaining VC++ 2015 64-bit build breaks

sandbox/win/src/policy_target_test.cc

 // Copyright (c) 2012 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 "base/memory/shared_memory.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_piece.h"
 #include "base/win/scoped_process_information.h"
 #include "base/win/windows_version.h"
 #include "sandbox/win/src/sandbox.h"
@@ skipping 364 matching lines @@
   wchar_t prog_name[MAX_PATH];
   GetModuleFileNameW(NULL, prog_name, MAX_PATH);
 
   TargetPolicy* policy = broker->CreatePolicy();
   void* shared_handle =
       policy->AddHandleToShare(read_only_view.handle().GetHandle());
 
   base::string16 arguments(L"\"");
   arguments += prog_name;
   arguments += L"\" -child 0 shared_memory_handle ";
+  // Cast through uintptr_t and then unsigned int to make the truncation
+  // explicit. Handles are size-of-pointer but are always 32-bit values.
   arguments += base::UintToString16(
-      reinterpret_cast<unsigned int>(shared_handle));
+      static_cast<unsigned int>(reinterpret_cast<uintptr_t>(shared_handle)));
 
   // Launch the app.
   ResultCode result = SBOX_ALL_OK;
   base::win::ScopedProcessInformation target;
 
   policy->SetTokenLevel(USER_INTERACTIVE, USER_LOCKDOWN);
   PROCESS_INFORMATION temp_process_info = {};
   result = broker->SpawnTarget(prog_name, arguments.c_str(), policy,
                                &temp_process_info);
   policy->Release();
 
   EXPECT_EQ(SBOX_ALL_OK, result);
   if (result == SBOX_ALL_OK)
     target.Set(temp_process_info);
 
   EXPECT_EQ(1, ::ResumeThread(target.thread_handle()));
 
   EXPECT_EQ(WAIT_TIMEOUT,
             ::WaitForSingleObject(target.process_handle(), 2000));
 
   EXPECT_TRUE(::TerminateProcess(target.process_handle(), 0));
 
   ::WaitForSingleObject(target.process_handle(), INFINITE);
 }
 
 }  // namespace sandbox