M59: Clear the PrintContext in WebLocalFrameImpl::Close().

M59: Clear the PrintContext in WebLocalFrameImpl::Close().

Also explicitly call PrintContext::EndPrintMode(), rather than calling
it in the destructor. Add a ScopedPrintMode helper class to do that
conveniently.

BUG=716474
Review-Url: https://codereview.chromium.org/2848823005
Cr-Commit-Position: refs/heads/master@{#468882}
(cherry picked from commit 85b7d7b31f25da2481ab2fa569c7b37a42abdeb6)

Review-Url: https://codereview.chromium.org/2864753004 .
Cr-Commit-Position: refs/branch-heads/3071@{#429}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/85199fb739f0c8b8e491cd6f1ac538efb4134ad0

[Lei Zhang, 2017-05-05 23:54:54]

Description was changed from

==========
M59: Clear the PrintContext in WebLocalFrameImpl::Close().

Also explicitly call PrintContext::EndPrintMode(), rather than calling
it in the destructor. Add a ScopedPrintMode helper class to do that
conveniently.

BUG=716474

Review-Url: https://codereview.chromium.org/2848823005
Cr-Commit-Position: refs/heads/master@{#468882}
(cherry picked from commit 85b7d7b31f25da2481ab2fa569c7b37a42abdeb6)
==========

to

==========
M59: Clear the PrintContext in WebLocalFrameImpl::Close().

Also explicitly call PrintContext::EndPrintMode(), rather than calling
it in the destructor. Add a ScopedPrintMode helper class to do that
conveniently.

BUG=716474

Review-Url: https://codereview.chromium.org/2848823005
Cr-Commit-Position: refs/heads/master@{#468882}
(cherry picked from commit 85b7d7b31f25da2481ab2fa569c7b37a42abdeb6)

Review-Url: https://codereview.chromium.org/2864753004 .
Cr-Commit-Position: refs/branch-heads/3071@{#429}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/85199fb739f0c8b8e491cd6f1ac5...
==========

[Lei Zhang, 2017-05-05 23:54:55]

Committed patchset #2 (id:20001) manually as
85199fb739f0c8b8e491cd6f1ac538efb4134ad0.