command_buffer_gles2: Implement EGL default Display as a global object

gpu/gles2_conform_support/egl/config.h

Index: gpu/gles2_conform_support/egl/config.h
diff --git a/gpu/gles2_conform_support/egl/config.h b/gpu/gles2_conform_support/egl/config.h
index 53bb56821812226be2f4e0c086e373a3f43f7c7f..1ce815648d9cf5f9324f1f0eecc8f6201354230d 100644
--- a/gpu/gles2_conform_support/egl/config.h
+++ b/gpu/gles2_conform_support/egl/config.h
@@ -13,10 +13,11 @@ namespace egl {
 
 class Config {
  public:
-  Config();
+  explicit Config(EGLint surface_type);
   ~Config();
-
+  bool Matches(const EGLint* attrib_list) const;
   bool GetAttrib(EGLint attribute, EGLint* value) const;
+  static bool ValidateAttributeList(const EGLint* attrib_list);
 
  private:
   // Total color component bits in the color buffer.