Use NV_draw_buffers to implement EXT_draw_buffers

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 65587ec03277791f3eaee02dacf077f0eb9a5a74..a6152956a58734f48b8fc5f0e58fc399be0f4aa7 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -2792,6 +2792,8 @@ bool GLES2DecoderImpl::InitializeShaderTranslator() {
     if (!draw_buffers_explicitly_enabled_)
       resources.MaxDrawBuffers = 1;
     resources.EXT_shader_texture_lod = shader_texture_lod_explicitly_enabled_;
+    resources.NV_draw_buffers =
+        draw_buffers_explicitly_enabled_ && features().nv_draw_buffers;
   } else {
     resources.OES_standard_derivatives =
         features().oes_standard_derivatives ? 1 : 0;
@@ -2805,6 +2807,8 @@ bool GLES2DecoderImpl::InitializeShaderTranslator() {
         features().ext_frag_depth ? 1 : 0;
     resources.EXT_shader_texture_lod =
         features().ext_shader_texture_lod ? 1 : 0;
+    resources.NV_draw_buffers =
+        features().nv_draw_buffers ? 1 : 0;
   }
 
   ShShaderSpec shader_spec = force_webgl_glsl_validation_ ? SH_WEBGL_SPEC