Add GL_CHROMIUM_screen_space_antialiasing to support alternative AA

gpu/command_buffer/common/gles2_cmd_format_autogen.h

 // Copyright 2014 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.
 
 // This file is auto-generated from
 // gpu/command_buffer/build_gles2_cmd_buffer.py
 // It's formatted by clang-format using chromium coding style:
 //    clang-format -i -style=chromium filename
 // DO NOT EDIT!
 
@@ skipping 14644 matching lines @@
   }
 
   gpu::CommandHeader header;
 };
 
 static_assert(sizeof(BlendBarrierKHR) == 4,
               "size of BlendBarrierKHR should be 4");
 static_assert(offsetof(BlendBarrierKHR, header) == 0,
               "offset of BlendBarrierKHR header should be 0");
 
+struct ApplyScreenSpaceAntialiasing {
+  typedef ApplyScreenSpaceAntialiasing ValueType;
+  static const CommandId kCmdId = kApplyScreenSpaceAntialiasing;
+  static const cmd::ArgFlags kArgFlags = cmd::kFixed;
+  static const uint8 cmd_flags = CMD_FLAG_SET_TRACE_LEVEL(3);
+
+  static uint32_t ComputeSize() {
+    return static_cast<uint32_t>(sizeof(ValueType));  // NOLINT
+  }
+
+  void SetHeader() { header.SetCmd<ValueType>(); }
+
+  void Init() { SetHeader(); }
+
+  void* Set(void* cmd) {
+    static_cast<ValueType*>(cmd)->Init();
+    return NextCmdAddress<ValueType>(cmd);
+  }
+
+  gpu::CommandHeader header;
+};
+
+static_assert(sizeof(ApplyScreenSpaceAntialiasing) == 4,
+              "size of ApplyScreenSpaceAntialiasing should be 4");
+static_assert(offsetof(ApplyScreenSpaceAntialiasing, header) == 0,
+              "offset of ApplyScreenSpaceAntialiasing header should be 0");
+
 #endif  // GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_FORMAT_AUTOGEN_H_