fix for high resolution timer on windows.

base/message_loop/message_loop.cc

Index: base/message_loop/message_loop.cc
diff --git a/base/message_loop/message_loop.cc b/base/message_loop/message_loop.cc
index 16b999c27845c3a6265372124bc632941339fa65..c01e5421bc3478605c5a0b16ef15d36a6bb9af78 100644
--- a/base/message_loop/message_loop.cc
+++ b/base/message_loop/message_loop.cc
@@ -616,8 +616,11 @@ bool MessageLoop::DoIdleWork() {
   // _if_ triggered by the timer happens with good resolution. If we don't
   // do this the default resolution is 15ms which might not be acceptable
   // for some tasks.
-  in_high_res_mode_ = pending_high_res_tasks_ > 0;
-  Time::ActivateHighResolutionTimer(in_high_res_mode_);
+  bool high_res = pending_high_res_tasks_ > 0;
+  if (high_res != in_high_res_mode_) {
+    in_high_res_mode_ = high_res;
+    Time::ActivateHighResolutionTimer(in_high_res_mode_);
+  }
 #endif
   return false;
 }