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This patch changes "4580583-{1,2}.html" to utilize |selection_test()| and
integrate into "4580583-1.html", since both tests use similar test input, for
ease of maintenance.

Following patch will rename "4580583-1.html" to
"insert_newline_in_quoted_content.html".

Note: "4580583-{1,2}.html" is failed on layout_ng bot due by pixel test.

Bug: 679977, 636993
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: Ie2eff78bee11cbc09f2bbdfa1f915b6cf662fe55
Reviewed-on: https://chromium-review.googlesource.com/991695
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548011}