assign kouhei@ as a loading && script expert.
I do not think <script type="text/html"> is a practical use-case, but if the same issue happens on other types, that can be a real problem.

It's very common to write GL shaders in a script tag that has a non-standard type, because we can easily embed shader source code in such a way and pass it as a string to the WebGL to compile it.

See https://www.html5rocks.com/en/tutorials/webgl/webgl_fundamentals/

But, I think this is still a low-priority issue.

FWIW, `<script type="text/html">` originated in the pre-HTML5 era:
https://www.html5rocks.com/en/tutorials/webcomponents/template/#toc-overloadingscript
It's still being used for browsers that don't support `<template>`.

From my analysis, this is primarily caused by script start tokens causing a background tokenizer flush and parser yield, which does a lot of thrashing on the message loop. This makes sense for JavaScript, but not for script elements which won't be executed in the first place (and thus don't require a yield for quicker renders).

I've posted a patch that avoids this behaviour for script types that ScriptLoader deems invalid for execution via HTMLTreeBuilderSimulator. This reduces the amount of time it takes for DOMContentLoaded in the script attachment from 367ms to 208ms, similar to the div attachment's 209ms on my machine.

https://chromium-review.googlesource.com/c/chromium/src/+/1247230

Thanks!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/174813503285a1ff88efe4fcb8775df6663fa371

commit 174813503285a1ff88efe4fcb8775df6663fa371
Author: Andrew Comminos <acomminos@fb.com>
Date: Tue Oct 02 04:16:23 2018

Only flush tokenized chunks to the HTML parser for valid script types.

Having a large amount of <script> tags on a page with an invalid type
for execution (e.g. text/html) triggers the same path for event loop
yielding as JavaScript tags, causing slowness due to parser yields and
unnecessarily aggressive chunking. Avoid performing this logic if the
ScriptLoader can't recognize the script type.

This reduces the amount of time it takes for DOMContentLoaded in the script
attachment for  issue 873648  from 367ms to 208ms, similar to the div attachment's
209ms.

R=kouhei@chromium.org

Bug:  873648 
Change-Id: I4c7ea76feb2034f5ff97fe08b481c790b9a35122
Reviewed-on: https://chromium-review.googlesource.com/1247230
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595719}
[modify] https://crrev.com/174813503285a1ff88efe4fcb8775df6663fa371/third_party/blink/renderer/core/html/parser/background_html_parser.cc
[modify] https://crrev.com/174813503285a1ff88efe4fcb8775df6663fa371/third_party/blink/renderer/core/html/parser/html_tree_builder_simulator.cc
[modify] https://crrev.com/174813503285a1ff88efe4fcb8775df6663fa371/third_party/blink/renderer/core/html/parser/html_tree_builder_simulator.h
[modify] https://crrev.com/174813503285a1ff88efe4fcb8775df6663fa371/third_party/blink/renderer/core/html/parser/html_tree_builder_simulator_test.cc