The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f544bbaa8a3564a1b47fb7fbad06b51348305b04

commit f544bbaa8a3564a1b47fb7fbad06b51348305b04
Author: Jian Li <jianli@chromium.org>
Date: Thu Oct 05 20:06:19 2017

Switch to disabling form control elements in loaded MHTML

We used to disable all form control elements when saving a page as
MHTML since the form in the MHTML document cannot be worked on due
to form submission and script execution disabled. As suggested by
Jeffrey Yasskin, we switched to disable form control elements in
the loaded MHTML document.

Bug:  771786 
Change-Id: I44b9c324192be052dd47db3d126a911ab5dd34e3
Reviewed-on: https://chromium-review.googlesource.com/701368
Commit-Queue: Jian Li <jianli@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506839}
[modify] https://crrev.com/f544bbaa8a3564a1b47fb7fbad06b51348305b04/third_party/WebKit/Source/core/exported/WebFrameSerializer.cpp
[modify] https://crrev.com/f544bbaa8a3564a1b47fb7fbad06b51348305b04/third_party/WebKit/Source/core/exported/WebFrameSerializerSanitizationTest.cpp
[modify] https://crrev.com/f544bbaa8a3564a1b47fb7fbad06b51348305b04/third_party/WebKit/Source/core/frame/MHTMLTest.cpp
[modify] https://crrev.com/f544bbaa8a3564a1b47fb7fbad06b51348305b04/third_party/WebKit/Source/core/html/HTMLFormControlElement.cpp
[delete] https://crrev.com/b0b6dfa9efe0a5109f486eb877de50574e34da42/third_party/WebKit/Source/core/testing/data/frameserialization/form.html
[add] https://crrev.com/f544bbaa8a3564a1b47fb7fbad06b51348305b04/third_party/WebKit/Source/core/testing/data/mhtml/form.mht