[LayoutNG] Dump NGPhysicalTextFragment

This patch dumps NGPhysicalTextFragment associated with LayoutText
in the same format as InlineTextBox to help reviewing test failures
in LayoutNG.

LayoutTreeAsText supports RootInlineBox and InlineFlowBox, but they
are not supported for LayoutNG yet. They may be added if they appear
a lot in the text failures, but I have not reviewed them yet.

Bug: 591099
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I80d6540794cc3630108e02d63a4f749e76e505d1
Reviewed-on: https://chromium-review.googlesource.com/864962
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#529371}
111 files changed