Revert r4473 to fix build breakage (local time zone tests failed)...

base/time_posix.cc

 // Copyright (c) 2006-2008 The Chromium 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 "base/time.h"
 
+#ifdef OS_MACOSX        
+#include <mach/mach_time.h>     
+#endif
 #include <sys/time.h>
 #include <time.h>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 
 namespace base {
 
 // The Time routines in this file use standard POSIX routines, or almost-
 // standard routines in the case of timegm.  We need to use a Mach-specific
@@ skipping 65 matching lines @@
   exploded->second       = timestruct.tm_sec;
   exploded->millisecond  = milliseconds % kMillisecondsPerSecond;
 }
 
 // TimeTicks ------------------------------------------------------------------
 
 // static
 TimeTicks TimeTicks::Now() {
   uint64_t absolute_micro;
 
-#if defined(OS_POSIX) && \
+#if defined(OS_MACOSX)
+  static mach_timebase_info_data_t timebase_info;       
+  if (timebase_info.denom == 0) {       
+    // Zero-initialization of statics guarantees that denom will be 0 before    
+    // calling mach_timebase_info.  mach_timebase_info will never set denom to  
+    // 0 as that would be invalid, so the zero-check can be used to determine   
+    // whether mach_timebase_info has already been called.  This is     
+    // recommended by Apple's QA1398.   
+    kern_return_t kr = mach_timebase_info(&timebase_info);      
+    DCHECK(kr == KERN_SUCCESS); 
+  }     
+
+  // mach_absolute_time is it when it comes to ticks on the Mac.  Other calls   
+  // with less precision (such as TickCount) just call through to       
+  // mach_absolute_time.        
+        
+  // timebase_info converts absolute time tick units into nanoseconds.  Convert 
+  // to microseconds up front to stave off overflows.   
+  absolute_micro = mach_absolute_time() / Time::kNanosecondsPerMicrosecond *    
+                   timebase_info.numer / timebase_info.denom;   
+        
+  // Don't bother with the rollover handling that the Windows version does.     
+  // With numer and denom = 1 (the expected case), the 64-bit absolute time     
+  // reported in nanoseconds is enough to last nearly 585 years.        
+        
+#elif defined(OS_POSIX) && \
       defined(_POSIX_MONOTONIC_CLOCK) && _POSIX_MONOTONIC_CLOCK >= 0
 
   struct timespec ts;
   if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0) {
     NOTREACHED() << "clock_gettime(CLOCK_MONOTONIC) failed.";
     return TimeTicks();
   }
 
   absolute_micro =
       (static_cast<int64>(ts.tv_sec) * Time::kMicrosecondsPerSecond) +
       (static_cast<int64>(ts.tv_nsec) / Time::kNanosecondsPerMicrosecond);
 
 #else  // _POSIX_MONOTONIC_CLOCK
 #error No usable tick clock function on this platform.
 #endif  // _POSIX_MONOTONIC_CLOCK
 
   return TimeTicks(absolute_micro);
 }
 
 // static
 TimeTicks TimeTicks::HighResNow() {
   return Now();
 }
 
 }  // namespace base