Read compositor VSync information from platform, when possible

ui/gl/sync_control_vsync_provider.cc

Index: ui/gl/sync_control_vsync_provider.cc
diff --git a/ui/gl/sync_control_vsync_provider.cc b/ui/gl/sync_control_vsync_provider.cc
index 16b1e8af9cdd8d453357ea4d2d35aa9c2e373993..49fa4715c214d4e52b5b3e85feef0a6901c09cef 100644
--- a/ui/gl/sync_control_vsync_provider.cc
+++ b/ui/gl/sync_control_vsync_provider.cc
@@ -10,11 +10,6 @@
 #include "base/time/time.h"
 
 #if defined(OS_LINUX)
-// These constants define a reasonable range for a calculated refresh interval.
-// Calculating refreshes out of this range will be considered a fatal error.
-const int64 kMinVsyncIntervalUs = base::Time::kMicrosecondsPerSecond / 400;
-const int64 kMaxVsyncIntervalUs = base::Time::kMicrosecondsPerSecond / 10;
-
 // How much noise we'll tolerate between successive computed intervals before
 // we think the latest computed interval is invalid (noisey due to
 // monitor configuration change, moving a window between monitors, etc.).
@@ -122,23 +117,8 @@ void SyncControlVSyncProvider::GetVSyncParameters(
     double relative_change =
         fabs(old_interval.InMillisecondsF() - new_interval.InMillisecondsF()) /
         new_interval.InMillisecondsF();
-    if (relative_change < kRelativeIntervalDifferenceThreshold) {
-      if (new_interval.InMicroseconds() < kMinVsyncIntervalUs ||
-          new_interval.InMicroseconds() > kMaxVsyncIntervalUs) {
-        LOG(FATAL) << "Calculated bogus refresh interval of "
-                   << new_interval.InMicroseconds() << " us. "
-                   << "Last time base of " << last_timebase_.ToInternalValue()
-                   << " us. "
-                   << "Current time base of " << timebase.ToInternalValue()
-                   << " us. "
-                   << "Last media stream count of "
-                   << last_media_stream_counter_ << ". "
-                   << "Current media stream count of " << media_stream_counter
-                   << ".";
-      } else {
-        last_good_interval_ = new_interval;
-      }
-    }
+    if (relative_change < kRelativeIntervalDifferenceThreshold)
+      last_good_interval_ = new_interval;

[piman, 2014/02/04 04:51:01]

I'd rather we either leave the LOG(FATAL) here, or we remove the logic to
estimate the rate from the intervals altogether.

[sheu, 2014/02/04 22:01:45]

We can't leave the LOG(FATAL) here -- that is the bug we're trying to fix, i.e.
in the case that we get a bogus interval here we can still rely on the interval
queried from the platform display manager (e.g. XRandR).

And we still need to leave the rate estimation in here for platforms that don't
currently run Ash (and for which we have no XRandR hookup).

   }
 
   last_timebase_ = timebase;