Revert 124144 - Sync trace time on Chrome OS (just like Android)

base/debug/trace_event_impl.cc

 // Copyright (c) 2012 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/debug/trace_event_impl.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
@@ skipping 669 matching lines @@
                                 const std::string& extra)
 {
 #if defined(OS_WIN)
   TraceEventETWProvider::Trace(name, phase, id, extra);
 #endif
   INTERNAL_TRACE_EVENT_ADD(phase, "ETW Trace Event", name,
                            TRACE_EVENT_FLAG_COPY, "id", id, "extra", extra);
 }
 
 void TraceLog::AddClockSyncMetadataEvents() {
-#if defined(OS_ANDROID) || defined(OS_CHROMEOS)
-  // Since Android/ChromeOS do not support sched_setaffinity, we cannot
-  // establish clock sync unless the scheduler clock is set to global.
-  // If the trace_clock file can't be read, we will assume the kernel
-  // doesn't support tracing and do nothing.
+#if defined(OS_ANDROID)
+  // Since Android does not support sched_setaffinity, we cannot establish clock
+  // sync unless the scheduler clock is set to global. If the trace_clock file
+  // can't be read, we will assume the kernel doesn't support tracing and do
+  // nothing.
   std::string clock_mode;
   if (!file_util::ReadFileToString(
           FilePath("/sys/kernel/debug/tracing/trace_clock"),
           &clock_mode))
     return;
 
   if (clock_mode != "local [global]\n") {
     DLOG(WARNING) <<
         "The kernel's tracing clock must be set to global in order for " <<
         "trace_event to be synchronized with . Do this by\n" <<
         "  echo global > /sys/kerel/debug/tracing/trace_clock";
     return;
   }
 
-  // Linux's kernel trace system has a trace_marker feature: this is a file on
+  // Android's kernel trace system has a trace_marker feature: this is a file on
   // debugfs that takes the written data and pushes it onto the trace
   // buffer. So, to establish clock sync, we write our monotonic clock into that
   // trace buffer.
   TimeTicks now = TimeTicks::HighResNow();
 
   double now_in_seconds = now.ToInternalValue() / 1000000.0;
   std::string marker =
       StringPrintf("trace_event_clock_sync: parent_ts=%f\n",
                    now_in_seconds);
   if (file_util::WriteFile(
@@ skipping 40 matching lines @@
   // Create a FNV hash from the process ID for XORing.
   // See http://isthe.com/chongo/tech/comp/fnv/ for algorithm details.
   unsigned long long offset_basis = 14695981039346656037ull;
   unsigned long long fnv_prime = 1099511628211ull;
   unsigned long long pid = static_cast<unsigned long long>(process_id_);
   process_id_hash_ = (offset_basis ^ pid) * fnv_prime;
 }
 
 }  // namespace debug
 }  // namespace base