Use double cast to avoid VS 2015 64-bit warning

If you convert a 64-bit pointer directly to a 32-bit or smaller integer
then VS 2015 guesses (not unreasonably) that it might be an accidental
pointer truncation. The standard fix is to use a double-cast, to a
pointer-sized integer and then to DWORD.

This fixes a C4311 "pointer truncation" warning introduced by
crrev.com/1225183003

Warning C4312 (conversion from int to ptr of greater size) is suppressed
in this project but adding double-casts for the reverse conversion keeps
the code symmetrical and allows us to enable C4312 in the future.

BUG=440500

Review URL: https://codereview.chromium.org/1684963003

Cr-Commit-Position: refs/heads/master@{#374828}

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;
   }
@@ -314,7 +314,8 @@ SBOX_TESTS_COMMAND int Process_CreateThread(int argc, wchar_t** argv) {
   DWORD thread_id = 0;
   HANDLE thread = NULL;
   thread = ::CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)&TestThreadFunc,
-                          reinterpret_cast<LPVOID>(pid), 0, &thread_id);
+                          reinterpret_cast<LPVOID>(static_cast<uintptr_t>(pid)),
+                          0, &thread_id);
 
   if (!thread) {
     return SBOX_TEST_THIRD_ERROR;
@@ -499,9 +500,9 @@ TEST(ProcessPolicyTest, TestCreateThreadOutsideSandbox) {
 
   DWORD thread_id = 0;
   HANDLE thread = NULL;
-  thread = TargetCreateThread(::CreateThread, NULL, 0,
-                              (LPTHREAD_START_ROUTINE)&TestThreadFunc,
-                              reinterpret_cast<LPVOID>(pid), 0, &thread_id);
+  thread = TargetCreateThread(
+      ::CreateThread, NULL, 0, (LPTHREAD_START_ROUTINE)&TestThreadFunc,
+      reinterpret_cast<LPVOID>(static_cast<uintptr_t>(pid)), 0, &thread_id);
   EXPECT_NE(static_cast<HANDLE>(NULL), thread);
   EXPECT_EQ(WAIT_OBJECT_0, WaitForSingleObject(thread, INFINITE));
   EXPECT_EQ(WAIT_OBJECT_0, WaitForSingleObject(event, INFINITE));