gl_gl_api_implemetation: DO API check instead of null fnptr checks

ui/gl/gl_gl_api_implementation.cc

 // Copyright (c) 2012 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.
 
 #include "ui/gl/gl_gl_api_implementation.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
@@ skipping 419 matching lines @@
 
 void RealGLApi::glDrawElementsFn(GLenum mode,
                                  GLsizei count,
                                  GLenum type,
                                  const void* indices) {
   if (!g_null_draw_bindings_enabled)
     GLApiBase::glDrawElementsFn(mode, count, type, indices);
 }
 
 void RealGLApi::glClearDepthFn(GLclampd depth) {
-  if (driver_->fn.glClearDepthFn) {
+  if (!version_->is_es) {
     GLApiBase::glClearDepthFn(depth);
   } else {
     DCHECK(driver_->fn.glClearDepthfFn);
     GLApiBase::glClearDepthfFn(static_cast<GLclampf>(depth));
   }
 }
 
 void RealGLApi::glDepthRangeFn(GLclampd z_near, GLclampd z_far) {
-  if (driver_->fn.glDepthRangeFn) {
+  if (!version_->is_es) {
     GLApiBase::glDepthRangeFn(z_near, z_far);
   } else {
+    DCHECK(driver_->fn.glDepthRangefFn);
     GLApiBase::glDepthRangefFn(static_cast<GLclampf>(z_near),
                                static_cast<GLclampf>(z_far));
   }
 }
 
 void RealGLApi::InitializeFilteredExtensions() {
   if (disabled_exts_.size()) {
     filtered_exts_.clear();
     if (WillUseGLGetStringForExtensions(this)) {
       filtered_exts_str_ =
@@ skipping 31 matching lines @@
 
 DebugGLApi::~DebugGLApi() {}
 
 NoContextGLApi::NoContextGLApi() {
 }
 
 NoContextGLApi::~NoContextGLApi() {
 }
 
 }  // namespace gl