Revert of High resolution timer fix for Windows

base/message_loop/incoming_task_queue.cc

Index: base/message_loop/incoming_task_queue.cc
diff --git a/base/message_loop/incoming_task_queue.cc b/base/message_loop/incoming_task_queue.cc
index 48c2f4202e13247ffcd27ee3c1eeeb6ce5e2aba4..bcc712b4a5d981b222b7a5ae4cbe84f9b67493e8 100644
--- a/base/message_loop/incoming_task_queue.cc
+++ b/base/message_loop/incoming_task_queue.cc
@@ -8,14 +8,12 @@
 #include "base/location.h"
 #include "base/message_loop/message_loop.h"
 #include "base/synchronization/waitable_event.h"
-#include "base/time/time.h"
 
 namespace base {
 namespace internal {
 
 IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
-    : high_res_task_count_(0),
-      message_loop_(message_loop),
+    : message_loop_(message_loop),
       next_sequence_num_(0) {
 }
 
@@ -27,23 +25,15 @@
   AutoLock locked(incoming_queue_lock_);
   PendingTask pending_task(
       from_here, task, CalculateDelayedRuntime(delay), nestable);
-#if defined(OS_WIN)
-  // We consider the task needs a high resolution timer if the delay is
-  // more than 0 and less than 32ms. This caps the relative error to
-  // less than 50% : a 33ms wait can wake at 48ms since the default
-  // resolution on Windows is between 10 and 15ms.
-  if (delay > TimeDelta() &&
-      delay.InMilliseconds() < (2 * Time::kMinLowResolutionThresholdMs)) {
-    ++high_res_task_count_;
-    pending_task.is_high_res = true;
-  }
-#endif
   return PostPendingTask(&pending_task);
 }
 
-bool IncomingTaskQueue::HasHighResolutionTasks() {
-  AutoLock lock(incoming_queue_lock_);
-  return high_res_task_count_ > 0;
+bool IncomingTaskQueue::IsHighResolutionTimerEnabledForTesting() {
+#if defined(OS_WIN)
+  return !high_resolution_timer_expiration_.is_null();
+#else
+  return true;
+#endif
 }
 
 bool IncomingTaskQueue::IsIdleForTesting() {
@@ -51,22 +41,29 @@
   return incoming_queue_.empty();
 }
 
-int IncomingTaskQueue::ReloadWorkQueue(TaskQueue* work_queue) {
+void IncomingTaskQueue::ReloadWorkQueue(TaskQueue* work_queue) {
   // Make sure no tasks are lost.
   DCHECK(work_queue->empty());
 
   // Acquire all we can from the inter-thread queue with one lock acquisition.
   AutoLock lock(incoming_queue_lock_);
   if (!incoming_queue_.empty())
-    incoming_queue_.Swap(work_queue);
+    incoming_queue_.Swap(work_queue);  // Constant time
 
-  // Reset the count of high resolution tasks since our queue is now empty.
-  int high_res_tasks = high_res_task_count_;
-  high_res_task_count_ = 0;
-  return high_res_tasks;
+  DCHECK(incoming_queue_.empty());
 }
 
 void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
+#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_ = TimeTicks();
+  }
+#endif
+
   AutoLock lock(incoming_queue_lock_);
   message_loop_ = NULL;
 }
@@ -78,10 +75,40 @@
 
 TimeTicks IncomingTaskQueue::CalculateDelayedRuntime(TimeDelta delay) {
   TimeTicks delayed_run_time;
-  if (delay > TimeDelta())
+  if (delay > TimeDelta()) {
     delayed_run_time = TimeTicks::Now() + delay;
-  else
+
+#if defined(OS_WIN)
+    if (high_resolution_timer_expiration_.is_null()) {
+      // Windows timers are granular to 15.6ms.  If we only set high-res
+      // timers for those under 15.6ms, then a 18ms timer ticks at ~32ms,
+      // which as a percentage is pretty inaccurate.  So enable high
+      // res timers for any timer which is within 2x of the granularity.
+      // This is a tradeoff between accuracy and power management.
+      bool needs_high_res_timers = delay.InMilliseconds() <
+          (2 * Time::kMinLowResolutionThresholdMs);
+      if (needs_high_res_timers) {
+        if (Time::ActivateHighResolutionTimer(true)) {
+          high_resolution_timer_expiration_ = TimeTicks::Now() +
+              TimeDelta::FromMilliseconds(
+                  MessageLoop::kHighResolutionTimerModeLeaseTimeMs);
+        }
+      }
+    }
+#endif
+  } else {
     DCHECK_EQ(delay.InMilliseconds(), 0) << "delay should not be negative";
+  }
+
+#if defined(OS_WIN)
+  if (!high_resolution_timer_expiration_.is_null()) {
+    if (TimeTicks::Now() > high_resolution_timer_expiration_) {
+      Time::ActivateHighResolutionTimer(false);
+      high_resolution_timer_expiration_ = TimeTicks();
+    }
+  }
+#endif
+
   return delayed_run_time;
 }