Reland "Linux perf tool support update + refactoring." (r22146, attempt #5)

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_BASE_PLATFORM_TIME_H_
 #define V8_BASE_PLATFORM_TIME_H_
 
 #include <time.h>
 #include <limits>
 
@@ skipping 297 matching lines @@
   // Returns a platform-dependent high-resolution tick count. Implementation
   // is hardware dependent and may or may not return sub-millisecond
   // resolution.  THIS CALL IS GENERALLY MUCH MORE EXPENSIVE THAN Now() AND
   // SHOULD ONLY BE USED WHEN IT IS REALLY NEEDED.
   // This method never returns a null TimeTicks.
   static TimeTicks HighResolutionNow();
 
   // Returns true if the high-resolution clock is working on this system.
   static bool IsHighResolutionClockWorking();
 
+  // Returns Linux kernel timestamp for generating profiler events. This method
+  // returns null TimeTicks if the kernel cannot provide the timestamps (e.g.,
+  // on non-Linux OS or if the kernel module for timestamps is not loaded).
+
+  static TimeTicks KernelTimestampNow();
+  static bool KernelTimestampAvailable();
+
   // Returns true if this object has not been initialized.
   bool IsNull() const { return ticks_ == 0; }
 
   // Converts to/from internal values. The meaning of the "internal value" is
   // completely up to the implementation, so it should be treated as opaque.
   static TimeTicks FromInternalValue(int64_t value) {
     return TimeTicks(value);
   }
   int64_t ToInternalValue() const {
     return ticks_;
@@ skipping 56 matching lines @@
   int64_t ticks_;
 };
 
 inline TimeTicks operator+(const TimeDelta& delta, const TimeTicks& ticks) {
   return ticks + delta;
 }
 
 } }  // namespace v8::base
 
 #endif  // V8_BASE_PLATFORM_TIME_H_