chore: cherry-pick f6cb89728f04 from chromium

[nornagon]

M85: Correctly retrieve the plugin when printing.

The logic in PrintRenderFrameHelper to retrieve a plugin is out of sync
with the logic in WebLocalFrameImpl::PrintBegin(). If
PrintRenderFrameHelper thinks it is printing a webpage, while
WebLocalFrameImpl thinks it is printing a plugin, bad things happen.

Fix this by adding WebLocalFrame::GetPluginToPrint(), to expose the
plugin finding logic in WebLocalFrameImpl. With GetPluginToPrint()
available, PrintRenderFrameHelper can delete its own GetPlugin() helper,
and switch the GetPlugin() callers to use GetPluginToPrint() instead.

Once synchronized, some use cases for printing Flash now work correctly.

(cherry picked from commit f8d7d428b1549ff1f87e3d34c5ca0b53d6ce4e84)

Tbr: japhet@chromium.org
Bug: 1098860
Change-Id: I9500db9ed2d6da0f87dad84c197f738d3a1e3c84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2317168
Reviewed-by: Nate Chapin japhet@chromium.org
Commit-Queue: Lei Zhang thestig@chromium.org
Cr-Original-Commit-Position: refs/heads/master@{#791564}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2324664
Reviewed-by: Lei Zhang thestig@chromium.org
Cr-Commit-Position: refs/branch-heads/4183@{#1009}
Cr-Branched-From: 740e9e8a40505392ba5c8e022a8024b3d018ca65-refs/heads/master@{#782793}

Notes: Security: backported fix for 1098860.

[nornagon]

CI failures unrelated; merging.

[release-clerk]

Release Notes Persisted

Security: backported fix for 1098860.