Enable high resolution time for TimeTicks::Now on Windows Canary

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 3680ee2a5e72478499a1079ac69af811d0a45c52..f35f735bfbd053196899d560b51110b2c3e2b76a 100644
--- a/base/time/time_win.cc
+++ b/base/time/time_win.cc
@@ -322,6 +322,12 @@ TimeDelta RolloverProtectedNow() {
   return TimeDelta::FromMilliseconds(now + rollover_ms);
 }
 
+bool IsBuggyAthlon(const base::CPU& cpu) {
+  // On Athlon X2 CPUs (e.g. model 15) QueryPerformanceCounter is
+  // unreliable.  Fallback to low-res clock.
+  return cpu.vendor_name() == "AuthenticAMD" && cpu.family() == 15;
+}
+
 // Overview of time counters:
 // (1) CPU cycle counter. (Retrieved via RDTSC)
 // The CPU counter provides the highest resolution time stamp and is the least
@@ -398,10 +404,8 @@ class HighResNowSingleton {
       skew_(0) {
     InitializeClock();
 
-    // On Athlon X2 CPUs (e.g. model 15) QueryPerformanceCounter is
-    // unreliable.  Fallback to low-res clock.
     base::CPU cpu;
-    if (cpu.vendor_name() == "AuthenticAMD" && cpu.family() == 15)
+    if (IsBuggyAthlon(cpu))
       DisableHighResClock();
   }
 
@@ -433,6 +437,24 @@ class HighResNowSingleton {
   friend struct DefaultSingletonTraits<HighResNowSingleton>;
 };
 
+TimeDelta HighResNowWrapper() {
+  return HighResNowSingleton::GetInstance()->Now();
+}
+
+typedef TimeDelta (*NowFunction)(void);
+NowFunction now_function = RolloverProtectedNow;
+
+bool CPUReliablySupportsHighResTime() {
+  base::CPU cpu;
+  if (!cpu.has_non_stop_time_stamp_counter())
+    return false;
+
+  if (IsBuggyAthlon(cpu))
+    return false;
+
+  return true;
+}
+
 }  // namespace
 
 // static
@@ -447,8 +469,18 @@ TimeTicks::TickFunctionType TimeTicks::SetMockTickFunction(
 }
 
 // static
+bool TimeTicks::SetNowIsHighResNowIfSupported() {
+  if (!CPUReliablySupportsHighResTime()) {
+    return false;
+  }
+
+  now_function = HighResNowWrapper;
+  return true;
+}
+
+// static
 TimeTicks TimeTicks::Now() {
-  return TimeTicks() + RolloverProtectedNow();
+  return TimeTicks() + now_function();
 }
 
 // static
@@ -483,6 +515,14 @@ bool TimeTicks::IsHighResClockWorking() {
   return HighResNowSingleton::GetInstance()->IsUsingHighResClock();
 }
 
+TimeTicks TimeTicks::UnprotectedNow() {
+  if (now_function == HighResNowWrapper) {
+    return Now();
+  } else {
+    return TimeTicks() + TimeDelta::FromMilliseconds(timeGetTime());
+  }
+}
+
 // TimeDelta ------------------------------------------------------------------
 
 // static