More reliable check for whether EGLSyncControlVSyncProvider should be instantiated.

ui/gl/sync_control_vsync_provider.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GL_SYNC_CONTROL_VSYNC_PROVIDER_H_
 #define UI_GL_SYNC_CONTROL_VSYNC_PROVIDER_H_
 
 #include <stdint.h>
 
 #include <queue>
 
 #include "base/macros.h"
 #include "ui/gfx/vsync_provider.h"
 
 namespace gl {
 
 // Base class for providers based on extensions like GLX_OML_sync_control and
 // EGL_CHROMIUM_sync_control.
 class SyncControlVSyncProvider : public gfx::VSyncProvider {
  public:
   SyncControlVSyncProvider();
   ~SyncControlVSyncProvider() override;
 
   void GetVSyncParameters(const UpdateVSyncCallback& callback) override;
 
+  static constexpr bool IsSupported() {
+#if defined(OS_LINUX)
+    return true;
+#else
+    return false;
+#endif  // defined(OS_LINUX)
+  }
+
  protected:
   virtual bool GetSyncValues(int64_t* system_time,
                              int64_t* media_stream_counter,
                              int64_t* swap_buffer_counter) = 0;
 
   virtual bool GetMscRate(int32_t* numerator, int32_t* denominator) = 0;
 
  private:
 #if defined(OS_LINUX)
   base::TimeTicks last_timebase_;
   uint64_t last_media_stream_counter_ = 0;
   base::TimeDelta last_good_interval_;
   bool invalid_msc_ = false;
 
   // A short history of the last few computed intervals.
   // We use this to filter out the noise in the computation resulting
   // from configuration change (monitor reconfiguration, moving windows
   // between monitors, suspend and resume, etc.).
   std::queue<base::TimeDelta> last_computed_intervals_;
 #endif  // defined(OS_LINUX)
 
   DISALLOW_COPY_AND_ASSIGN(SyncControlVSyncProvider);
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_SYNC_CONTROL_VSYNC_PROVIDER_H_