Add a mechanism for command buffer to conditionally allow ES3 enums.

gpu/command_buffer/service/gles2_cmd_validation.h

Index: gpu/command_buffer/service/gles2_cmd_validation.h
diff --git a/gpu/command_buffer/service/gles2_cmd_validation.h b/gpu/command_buffer/service/gles2_cmd_validation.h
index 22ee2da0d0d7c424f59eae562d9cb6d4cecf1aa0..8ca98613d725b7882b4084b7bd1aeb9113c15c2d 100644
--- a/gpu/command_buffer/service/gles2_cmd_validation.h
+++ b/gpu/command_buffer/service/gles2_cmd_validation.h
@@ -22,9 +22,7 @@ class ValueValidator {
   ValueValidator() {}
 
   ValueValidator(const T* valid_values, int num_values) {
-    for (int ii = 0; ii < num_values; ++ii) {
-      AddValue(valid_values[ii]);
-    }
+    AddValues(valid_values, num_values);
   }
 
   void AddValue(const T value) {
@@ -33,6 +31,12 @@ class ValueValidator {
     }
   }
 
+  void AddValues(const T* valid_values, int num_values) {
+    for (int ii = 0; ii < num_values; ++ii) {
+      AddValue(valid_values[ii]);
+    }
+  }
+
   bool IsValid(const T value) const {
     return std::find(valid_values_.begin(), valid_values_.end(), value) !=
            valid_values_.end();
@@ -48,6 +52,9 @@ class ValueValidator {
 
 struct Validators {
   Validators();
+
+  void AddES3Values();
+
 #include "gpu/command_buffer/service/gles2_cmd_validation_autogen.h"
 };