Fix use_image_texture_target inconsistencies

cc/proto/renderer_settings.proto

 // Copyright 2015 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.
 
 syntax = "proto2";
 
 package cc.proto;
 
 option optimize_for = LITE_RUNTIME;
 
+message UseImageTextureTargets {
+  optional uint32 buffer_usage = 1;

[erikchen, 2016/07/15 21:08:35]

should these be required?

[ericrk, 2016/07/19 20:22:43]

Although these are "required", we use optional for all fields, as using required
makes deprecating fields much harder.

+  optional uint32 buffer_format = 2;
+  optional uint32 texture_target = 3;
+};
+
 message RendererSettings {
   optional bool allow_antialiasing = 1;
   optional bool force_antialiasing = 2;
   optional bool force_blending_with_shaders = 3;
   optional bool partial_swap_enabled = 4;
   optional bool finish_rendering_on_resize = 5;
   optional bool should_clear_root_render_pass = 6;
   optional bool disable_display_vsync = 7;
   optional bool release_overlay_resources_after_gpu_query = 8;
   optional double refresh_rate = 9;
   optional uint32 highp_threshold_min = 10;
   optional uint32 texture_id_allocation_chunk_size = 11;
   optional bool use_gpu_memory_buffer_resources = 12;
   optional uint32 preferred_tile_format = 13;
+  repeated UseImageTextureTargets use_image_texture_targets = 14;
 }