gl_gl_api_implemetation: DO API check instead of null fnptr checks

ui/gl/gl_gl_api_implementation.cc

Index: ui/gl/gl_gl_api_implementation.cc
diff --git a/ui/gl/gl_gl_api_implementation.cc b/ui/gl/gl_gl_api_implementation.cc
index cc4453ea910464274308768dfb8a9dcc9e77dc71..00d756a74b11e667b03b0eca762272fff4bf76a9 100644
--- a/ui/gl/gl_gl_api_implementation.cc
+++ b/ui/gl/gl_gl_api_implementation.cc
@@ -437,7 +437,7 @@ void RealGLApi::glDrawElementsFn(GLenum mode,
 }
 
 void RealGLApi::glClearDepthFn(GLclampd depth) {
-  if (driver_->fn.glClearDepthFn) {
+  if (!version_->is_es) {
     GLApiBase::glClearDepthFn(depth);
   } else {
     DCHECK(driver_->fn.glClearDepthfFn);
@@ -446,9 +446,10 @@ void RealGLApi::glClearDepthFn(GLclampd 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));
   }