Move platform abstraction to base library

src/base/platform/time.h

 // 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.
 
-#ifndef V8_PLATFORM_TIME_H_
-#define V8_PLATFORM_TIME_H_
+#ifndef V8_BASE_PLATFORM_TIME_H_
+#define V8_BASE_PLATFORM_TIME_H_
 
 #include <time.h>
 #include <limits>
 
 #include "src/base/macros.h"
 
 // Forward declarations.
 extern "C" {
 struct _FILETIME;
 struct mach_timespec;
 struct timespec;
 struct timeval;
 }
 
 namespace v8 {
-namespace internal {
+namespace base {
 
 class Time;
 class TimeTicks;
 
 // -----------------------------------------------------------------------------
 // TimeDelta
 //
 // This class represents a duration of time, internally represented in
 // microseonds.
 
@@ skipping 348 matching lines @@
   explicit TimeTicks(int64_t ticks) : ticks_(ticks) {}
 
   // Tick count in microseconds.
   int64_t ticks_;
 };
 
 inline TimeTicks operator+(const TimeDelta& delta, const TimeTicks& ticks) {
   return ticks + delta;
 }
 
-} }  // namespace v8::internal
+} }  // namespace v8::base
 
-#endif  // V8_PLATFORM_TIME_H_
+#endif  // V8_BASE_PLATFORM_TIME_H_