Add -Wshorten-64-to-32 flag to mac builds.

src/base/platform/time.cc

 // Copyright 2013 the V8 project 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 "src/base/platform/time.h"
 
 #if V8_OS_POSIX
 #include <fcntl.h>  // for O_RDONLY
 #include <sys/time.h>
 #include <unistd.h>
@@ skipping 93 matching lines @@
   DCHECK_LT(ts.tv_nsec,
             static_cast<long>(Time::kNanosecondsPerSecond));  // NOLINT
   return TimeDelta(ts.tv_sec * Time::kMicrosecondsPerSecond +
                    ts.tv_nsec / Time::kNanosecondsPerMicrosecond);
 }
 
 
 struct mach_timespec TimeDelta::ToMachTimespec() const {
   struct mach_timespec ts;
   DCHECK(delta_ >= 0);
-  ts.tv_sec = delta_ / Time::kMicrosecondsPerSecond;
+  ts.tv_sec = static_cast<unsigned>(delta_ / Time::kMicrosecondsPerSecond);
   ts.tv_nsec = (delta_ % Time::kMicrosecondsPerSecond) *
       Time::kNanosecondsPerMicrosecond;
   return ts;
 }
 
 #endif  // V8_OS_MACOSX
 
 
 #if V8_OS_POSIX
 
@@ skipping 513 matching lines @@
 
 
 // static
 bool TimeTicks::KernelTimestampAvailable() {
   return kernel_tick_clock.Pointer()->Available();
 }
 
 #endif  // V8_OS_WIN
 
 } }  // namespace v8::base