Extract the mini_installer's entrypoint into its own source file.

chrome/installer/mini_installer/mini_installer_exe_main.cc

+// Copyright 2017 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 <stdint.h>
+
+#include "chrome/installer/mini_installer/mini_installer.h"
+
+// http://blogs.msdn.com/oldnewthing/archive/2004/10/25/247180.aspx
+extern "C" IMAGE_DOS_HEADER __ImageBase;
+
+extern "C" int __stdcall MainEntryPoint() {
+  mini_installer::ProcessExitResult result =
+      mini_installer::WMain(reinterpret_cast<HMODULE>(&__ImageBase));
+  ::ExitProcess(result.exit_code);
+}
+
+#if defined(ADDRESS_SANITIZER)
+// Executables instrumented with ASAN need CRT functions. We do not use
+// the /ENTRY switch for ASAN instrumented executable and a "main" function
+// is required.
+extern "C" int WINAPI wWinMain(HINSTANCE /* instance */,
+                               HINSTANCE /* previous_instance */,
+                               LPWSTR /* command_line */,
+                               int /* command_show */) {
+  return MainEntryPoint();
+}
+#endif
+
+// VC Express editions don't come with the memset CRT obj file and linking to
+// the obj files between versions becomes a bit problematic. Therefore,
+// simply implement memset.
+//
+// This also avoids having to explicitly set the __sse2_available hack when
+// linking with both the x64 and x86 obj files which is required when not
+// linking with the std C lib in certain instances (including Chromium) with
+// MSVC.  __sse2_available determines whether to use SSE2 intructions with
+// std C lib routines, and is set by MSVC's std C lib implementation normally.
+extern "C" {
+#pragma function(memset)
+void* memset(void* dest, int c, size_t count) {
+  uint8_t* scan = reinterpret_cast<uint8_t*>(dest);
+  while (count--)
+    *scan++ = static_cast<uint8_t>(c);
+  return dest;
+}
+}  // extern "C"