gl: Disable SGI_video_sync by default.

ui/gl/gl_surface_glx.cc

Index: ui/gl/gl_surface_glx.cc
diff --git a/ui/gl/gl_surface_glx.cc b/ui/gl/gl_surface_glx.cc
index 47d32319543a9c50e8129915fb4e92cad268623e..1ae6678bc7c50aec287e3c0430ba31f8a87da4c2 100644
--- a/ui/gl/gl_surface_glx.cc
+++ b/ui/gl/gl_surface_glx.cc
@@ -9,6 +9,7 @@ extern "C" {
 }
 #include <memory>
 
+#include "base/command_line.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/macros.h"
@@ -500,10 +501,24 @@ bool NativeViewGLSurfaceGLX::Initialize(GLSurface::Format format) {
   DCHECK(config_);
   glx_window_ = glXCreateWindow(g_display, config_, window_, NULL);
 
-  if (g_glx_oml_sync_control_supported)
+  if (g_glx_oml_sync_control_supported) {
     vsync_provider_.reset(new OMLSyncControlVSyncProvider(glx_window_));
-  else if (g_glx_sgi_video_sync_supported)
+  } else if (g_glx_sgi_video_sync_supported &&
+             base::CommandLine::ForCurrentProcess()->HasSwitch(
+               switches::kEnableSgiVideoSync)) {
     vsync_provider_.reset(new SGIVideoSyncVSyncProvider(config_, glx_window_));
+  } else {
+    // Assume a refresh rate of 59.9 Hz, which will cause us to skip
+    // 1 frame every 10 seconds on a 60Hz monitor, but will prevent us
+    // from blocking the GPU service due to back pressure. This would still
+    // encounter backpressure on a <60Hz monitor, but hopefully that is
+    // not common.

[piman, 2016/08/24 21:04:29]

The investigation for bug
https://bugs.chromium.org/p/chromium/issues/detail?id=262437 (where we would
reduce frame rate to 30Hz when the monitor was anywhere below 60) showed that
it's very common unfortunately. 50 or 55Hz is probably a safer lower bound (at
the cost of more missed frames).

We used to have a UMA histogram for the refresh rate
(GPU.AcceleratedSurfaceRefreshRate) but apparently it broke eons ago.

[danakj, 2016/08/24 22:20:50]

Why not just grab the actual refresh rate here? We have an x display. It looks
like this gives an int instead of something more accurate, but maybe good
enough?

int event, error;
int fps = 50;
if (XRRQueryExtension(&event, &error)) {
  XRRScreenConfiguration *conf = XRRGetScreenInfo(g_display, parent_window_);
  fps = XRRConfigCurrentRate(conf);
  XRRFreeScreenConfigInfo(conf);
}

+    const base::TimeTicks kDefaultTimebase;
+    const base::TimeDelta kDefaultInterval =
+        base::TimeDelta::FromSeconds(1) / 59.9;
+    vsync_provider_.reset(
+        new gfx::VSyncProviderStub(kDefaultTimebase, kDefaultInterval));
+  }
 
   return true;
 }