DevTools: Network preview for HTML frame-title rule violation

Accessibility Insights identifies an issue in which the iframe
which contains the HTML preview of network requests does not have
a title, which could present a difficulty for assistive technology.
Because, particularly among HTML content, it's highly likely that
the HTML content is going to be presented on the web application,
and the preview itself is not intended to be interactive, this
change adds a role="presentation" attribute. This is intended to
make the element semantically meaningless to assistive tech [1].

[1] https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/ARIA_Techniques/Using_the_presentation_role

Bug: 963183
Change-Id: I0f0fd02b13595f4787ebf0919abe8cf5a721884e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1841940Reviewed-by: Lorne Mitchell <lomitch@microsoft.com>
Commit-Queue: Robert Paveza <Rob.Paveza@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#703997}

third_party/blink/renderer/devtools/front_end/network/RequestHTMLView.js

@@ -65,6 +65,7 @@ Network.RequestHTMLView = class extends UI.VBox {
     iframe.setAttribute('sandbox', '');  // Forbid to run JavaScript and set unique origin.
     iframe.setAttribute('src', this._dataURL);
     iframe.setAttribute('tabIndex', -1);
+    UI.ARIAUtils.markAsPresentation(iframe);
     this.contentElement.appendChild(iframe);
   }
 };