ui: Prefer +/- operators to apply offsets.

ui/gl/gl_surface_glx.h

Index: ui/gl/gl_surface_glx.h
diff --git a/ui/gl/gl_surface_glx.h b/ui/gl/gl_surface_glx.h
index 908c2fb95e85fe5a94d9c7f54765646b085d7b8d..76a8f8197ef27c6562761bc940b1c201367bf3f8 100644
--- a/ui/gl/gl_surface_glx.h
+++ b/ui/gl/gl_surface_glx.h
@@ -5,6 +5,8 @@
 #ifndef UI_GL_GL_SURFACE_GLX_H_
 #define UI_GL_GL_SURFACE_GLX_H_
 
+#include <string>
+
 #include "base/compiler_specific.h"
 #include "ui/base/x/x11_util.h"
 #include "ui/gfx/native_widget_types.h"
@@ -59,8 +61,15 @@ class GL_EXPORT NativeViewGLSurfaceGLX : public GLSurfaceGLX {
   virtual std::string GetExtensions() OVERRIDE;
   virtual void* GetConfig() OVERRIDE;
   virtual bool PostSubBuffer(int x, int y, int width, int height) OVERRIDE;
-  virtual bool GetVSyncParameters(base::TimeTicks* timebase,
-                                  base::TimeDelta* interval) OVERRIDE;
+  virtual void GetVSyncParameters(const UpdateVSyncCallback& callback) OVERRIDE;
+
+  class VSyncProvider {
+   public:
+    virtual ~VSyncProvider() { }
+
+    virtual void GetVSyncParameters(
+        const GLSurface::UpdateVSyncCallback& callback) = 0;
+  };
 
  protected:
   NativeViewGLSurfaceGLX();
@@ -72,6 +81,8 @@ class GL_EXPORT NativeViewGLSurfaceGLX : public GLSurfaceGLX {
   void* config_;
   gfx::Size size_;
 
+  scoped_ptr<VSyncProvider> vsync_provider_;
+
   DISALLOW_COPY_AND_ASSIGN(NativeViewGLSurfaceGLX);
 };