3 files changed, 43 insertions, 8 deletions

diff --git a/base/message_loop.cc b/base/message_loop.cc
index 8f6c997b..0b03d3c 100644
--- a/base/message_loop.cc
+++ b/base/message_loop.cc
@@ -179,6 +179,16 @@ MessageLoop::~MessageLoop() {
 
   // OK, now make it so that no one can find us.
   lazy_tls_ptr.Pointer()->Set(NULL);
+
+#if defined(OS_WIN)
+  // If we left the high-resolution timer activated, deactivate it now.
+  // Doing this is not-critical, it is mainly to make sure we track
+  // the high resolution timer activations properly in our unit tests.
+  if (!high_resolution_timer_expiration_.is_null()) {
+    Time::ActivateHighResolutionTimer(false);
+    high_resolution_timer_expiration_ = base::TimeTicks();
+  }
+#endif
 }
 
 void MessageLoop::AddDestructionObserver(
@@ -337,9 +347,10 @@ void MessageLoop::PostTask_Helper(
       bool needs_high_res_timers =
           delay_ms < (2 * Time::kMinLowResolutionThresholdMs);
       if (needs_high_res_timers) {
-        Time::ActivateHighResolutionTimer(true);
-        high_resolution_timer_expiration_ = base::TimeTicks::Now() +
-            TimeDelta::FromMilliseconds(kHighResolutionTimerModeLeaseTimeMs);
+        if (Time::ActivateHighResolutionTimer(true)) {
+          high_resolution_timer_expiration_ = base::TimeTicks::Now() +
+              TimeDelta::FromMilliseconds(kHighResolutionTimerModeLeaseTimeMs);
+        }
       }
     }
 #endif
diff --git a/base/time.h b/base/time.h
index 79e30b4..305ca6b 100644
--- a/base/time.h
+++ b/base/time.h
@@ -283,10 +283,16 @@ class Time {
   // Activates or deactivates the high resolution timer based on the |activate|
   // flag.  If the HighResolutionTimer is not Enabled (see
   // EnableHighResolutionTimer), this function will return false.  Otherwise
-  // returns true.
+  // returns true.  Each successful activate call must be paired with a
+  // subsequent deactivate call.
   // All callers to activate the high resolution timer must eventually call
   // this function to deactivate the high resolution timer.
   static bool ActivateHighResolutionTimer(bool activate);
+
+  // Returns true if the high resolution timer is both enabled and activated.
+  // This is provided for testing only, and is not tracked in a thread-safe
+  // way.
+  static bool IsHighResolutionTimerInUse();
 #endif
 
   // Converts an exploded structure representing either the local time or UTC
@@ -405,6 +411,9 @@ class Time {
   // when using battery power, we might elect to prevent high speed timers
   // which would draw more power.
   static bool high_resolution_timer_enabled_;
+  // Count of activations on the high resolution timer.  Only use in tests
+  // which are single threaded.
+  static int high_resolution_timer_activated_;
 #endif
 
   // Time in microseconds in UTC.
diff --git a/base/time_win.cc b/base/time_win.cc
index 5d3ecd6..502dd83 100644
--- a/base/time_win.cc
+++ b/base/time_win.cc
@@ -99,6 +99,7 @@ void InitializeClock() {
 const int64 Time::kTimeTToMicrosecondsOffset = GG_INT64_C(11644473600000000);
 
 bool Time::high_resolution_timer_enabled_ = false;
+int Time::high_resolution_timer_activated_ = 0;
 
 // static
 Time Time::Now() {
@@ -162,22 +163,36 @@ void Time::EnableHighResolutionTimer(bool enable) {
 }
 
 // static
-bool Time::ActivateHighResolutionTimer(bool activate) {
-  if (!high_resolution_timer_enabled_)
+bool Time::ActivateHighResolutionTimer(bool activating) {
+  if (!high_resolution_timer_enabled_ && activating)
     return false;
 
   // Using anything other than 1ms makes timers granular
   // to that interval.
   const int kMinTimerIntervalMs = 1;
   MMRESULT result;
-  if (activate)
+  if (activating) {
     result = timeBeginPeriod(kMinTimerIntervalMs);
-  else
+    high_resolution_timer_activated_++;
+  } else {
     result = timeEndPeriod(kMinTimerIntervalMs);
+    high_resolution_timer_activated_--;
+  }
   return result == TIMERR_NOERROR;
 }
 
 // static
+bool Time::IsHighResolutionTimerInUse() {
+  // Note:  we should track the high_resolution_timer_activated_ value
+  // under a lock if we want it to be accurate in a system with multiple
+  // message loops.  We don't do that - because we don't want to take the
+  // expense of a lock for this.  We *only* track this value so that unit
+  // tests can see if the high resolution timer is on or off.
+  return high_resolution_timer_enabled_ &&
+      high_resolution_timer_activated_ > 0;
+}
+
+// static
 Time Time::FromExploded(bool is_local, const Exploded& exploded) {
   // Create the system struct representing our exploded time. It will either be
   // in local time or UTC.