gl: Disable SGI_video_sync by default.

ui/gfx/vsync_provider.h

Index: ui/gfx/vsync_provider.h
diff --git a/ui/gfx/vsync_provider.h b/ui/gfx/vsync_provider.h
index 90464bcbf6841ec89840fcca970756338ff39b21..74542fb3d8034393d346daf3ee526585a6d2cf4a 100644
--- a/ui/gfx/vsync_provider.h
+++ b/ui/gfx/vsync_provider.h
@@ -28,6 +28,22 @@ class GFX_EXPORT VSyncProvider {
   virtual void GetVSyncParameters(const UpdateVSyncCallback& callback) = 0;
 };
 
+// Provides a contant timebase and interval.
+class GFX_EXPORT FixedVSyncProvider : public VSyncProvider {

[sunnyps, 2016/08/25 01:59:29]

Do we even need FixedVSyncProvider? If a vsync provider is not present the
synthetic BFS will use BeginFrameArgs::DefaultInterval (16667 us) so just
modifying that should be sufficient, no?

[danakj, 2016/08/25 02:04:52]

BeginFrameArgs::DefaultInterval is used all over the place tho, right? I find
changing that for branching to be scary.

[brianderson, 2016/08/25 05:09:50]

I did it this way because I like the decision to use a fixed provider to be
explicit and in the same place where the other vsync providers are being
selected, but Dana makes a good point about branching.

Going to keep this as-is for now.

+ public:
+  FixedVSyncProvider(base::TimeTicks timebase, base::TimeDelta interval)
+    : timebase_(timebase), interval_(interval) {
+  }
+
+  ~FixedVSyncProvider() override {}
+
+  void GetVSyncParameters(const UpdateVSyncCallback& callback) override;
+
+ private:
+  base::TimeTicks timebase_;
+  base::TimeDelta interval_;
+};
+
 }  // namespace gfx
 
 #endif  // UI_GFX_VSYNC_PROVIDER_H_