Use double cast to avoid VS 2015 64-bit warning

sandbox/win/src/process_policy_test.cc

Index: sandbox/win/src/process_policy_test.cc
diff --git a/sandbox/win/src/process_policy_test.cc b/sandbox/win/src/process_policy_test.cc
index d272e624cc096b8d711a517bd4adcf14d0a16fe9..4f1003b05ed3123806392d9e74f07e65ff3c69ad 100644
--- a/sandbox/win/src/process_policy_test.cc
+++ b/sandbox/win/src/process_policy_test.cc
@@ -284,8 +284,8 @@ std::wstring GenerateEventName(DWORD pid) {
 // This is the function that is called when testing thread creation.
 // It is expected to set an event that the caller is waiting on.
 DWORD TestThreadFunc(LPVOID lpdwThreadParam) {
-  std::wstring event_name =
-      GenerateEventName(reinterpret_cast<DWORD>(lpdwThreadParam));
+  std::wstring event_name = GenerateEventName(
+      static_cast<DWORD>(reinterpret_cast<uintptr_t>(lpdwThreadParam)));
   if (!event_name.length()) {
     return 1;
   }