Make surface GetFormat pure virtual, add missing overrides.

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 37ef1103c1fdde836dde4b14c509e3d1b3e1d4fe..d5f282dabb29e1c6734dcb9c59772f16170dd4db 100644
--- a/ui/gl/gl_surface_glx.cc
+++ b/ui/gl/gl_surface_glx.cc
@@ -616,6 +616,10 @@ void* NativeViewGLSurfaceGLX::GetConfig() {
   return config_;
 }
 
+GLSurfaceFormat NativeViewGLSurfaceGLX::GetFormat() {
+  return GLSurfaceFormat();
+}
+
 unsigned long NativeViewGLSurfaceGLX::GetCompatibilityKey() {
   return visual_id_;
 }
@@ -709,6 +713,10 @@ void* UnmappedNativeViewGLSurfaceGLX::GetConfig() {
   return config_;
 }
 
+GLSurfaceFormat UnmappedNativeViewGLSurfaceGLX::GetFormat() {
+  return GLSurfaceFormat();
+}
+
 unsigned long UnmappedNativeViewGLSurfaceGLX::GetCompatibilityKey() {
   return XVisualIDFromVisual(g_visual);
 }