Enforce no uncleared OES external textures. Clear in AVDA, not GVD.

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 c480b71567dca3814c19aeca0b4f7185bc338e42..8314a238f677e347c27d2c0a5af30342df5aca6a 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -12183,7 +12183,8 @@ bool GLES2DecoderImpl::ClearLevel(Texture* texture,
                                   int yoffset,
                                   int width,
                                   int height) {
-  DCHECK(target != GL_TEXTURE_3D && target != GL_TEXTURE_2D_ARRAY);
+  DCHECK(target != GL_TEXTURE_3D && target != GL_TEXTURE_2D_ARRAY &&
+         target != GL_TEXTURE_EXTERNAL_OES);
   uint32_t channels = GLES2Util::GetChannelsForFormat(format);
   if ((feature_info_->feature_flags().angle_depth_texture ||
        feature_info_->IsWebGL2OrES3Context())