Fix more disabled MSVC warnings, base/ edition.

base/threading/platform_thread_win.cc

Index: base/threading/platform_thread_win.cc
diff --git a/base/threading/platform_thread_win.cc b/base/threading/platform_thread_win.cc
index 80f353a8b46f3a7c8241cb2247ec252037ec2ca8..3df371943f5e6fdf1a91175802b7fb36f78d9aba 100644
--- a/base/threading/platform_thread_win.cc
+++ b/base/threading/platform_thread_win.cc
@@ -150,9 +150,8 @@ void PlatformThread::Sleep(TimeDelta duration) {
   // When measured with a high resolution clock, Sleep() sometimes returns much
   // too early. We may need to call it repeatedly to get the desired duration.
   TimeTicks end = TimeTicks::Now() + duration;
-  TimeTicks now;
-  while ((now = TimeTicks::Now()) < end)
-    ::Sleep((end - now).InMillisecondsRoundedUp());
+  for (TimeTicks now = TimeTicks::Now(); now < end; now = TimeTicks::Now())
+    ::Sleep(static_cast<DWORD>((end - now).InMillisecondsRoundedUp()));
 }
 
 // static