Makes TraceTicks use lowres times on Win when highres are buggy or slow

base/time/time_win.cc

Index: base/time/time_win.cc
diff --git a/base/time/time_win.cc b/base/time/time_win.cc
index e9044603e9aedf7a7841d6f2e8406ad68289f291..1897b04995bb9cb916860b4db67ea29f35db5940 100644
--- a/base/time/time_win.cc
+++ b/base/time/time_win.cc
@@ -436,22 +436,19 @@ void InitializeNowFunctionPointers() {
   // TraceTicks::Now() must use the low-resolution clock.
   //
   // If the QPC implementation is expensive and/or unreliable, TimeTicks::Now()
-  // will use the low-resolution clock, but TraceTicks::Now() will use the QPC
-  // (in the hope that it is still useful for tracing purposes). A CPU lacking a
-  // non-stop time counter will cause Windows to provide an alternate QPC
-  // implementation that works, but is expensive to use. Certain Athlon CPUs are
-  // known to make the QPC implementation unreliable.
+  // and TraceTicks::Now() will still use the low-resolution clock. A CPU
+  // lacking a non-stop time counter will cause Windows to provide an alternate
+  // QPC implementation that works, but is expensive to use. Certain Athlon CPUs
+  // are known to make the QPC implementation unreliable.
   //
   // Otherwise, both Now functions can use the high-resolution QPC clock. As of
-  // 4 January 2015, ~68% of users fall within this category.
+  // 21 August 2015, ~72% of users fall within this category.
   NowFunction now_function;
   NowFunction system_trace_now_function;
   base::CPU cpu;
-  if (ticks_per_sec.QuadPart <= 0) {
+  if (ticks_per_sec.QuadPart <= 0 ||
+      !cpu.has_non_stop_time_stamp_counter() || IsBuggyAthlon(cpu)) {
     now_function = system_trace_now_function = &RolloverProtectedNow;

[fmeawad, 2015/08/21 21:24:40]

Can you explain why you still need 2 variable (now_function and
system_trace_now_function)

-  } else if (!cpu.has_non_stop_time_stamp_counter() || IsBuggyAthlon(cpu)) {
-    now_function = &RolloverProtectedNow;
-    system_trace_now_function = &QPCNow;
   } else {
     now_function = system_trace_now_function = &QPCNow;
   }