Improve fallback for Burmese with leading punctuation + spacing mark

Improve fallback for Burmese with leading punctuation + spacing mark

Reland after revert in 1b8f4236e2dbf4e07bf0171300003168633b8660,
previous CL https://codereview.chromium.org/2530153002/
Previously failing Win10 test needs a rebaseline.

Issue 618178 describes an example where a Burmese text run starts with a
leading punctuation character followed by a combining spacing mark. This
grapheme cannot be shaped with the default font, since Times for example
cannot display the combination of a left quote with a Burmese combining
mark. Our fallback code attempts to find a fallback font based on the
first character at the beginning of an extracted unshaped sub-run, which
does not lead to finding a font suitable for Myanmar text in this case.
So in a way it runs into a fallback trap, where no fallback hint helps
to find the right fallback font and the whole run ends up as notdef
glyphs.

This CL attempts to resolve this by looking for a better fallback hint
character, which is not script common or inherited, if such is
available. This improves the situation for the Burmese text from the
issue report.

In addition, as a better fix we should give higher importance to the
locale information in font fallback, filed as issue 668706.

BUG=618178
TBR=eae,kojii,behdad

Committed: https://crrev.com/04f5eaaa234b142614e315f3ccd94f4e55015f10
Cr-Commit-Position: refs/heads/master@{#434944}

[drott, 2016-11-29 08:50:51]

The CQ bit was checked by drott@chromium.org

[commit-bot: I haz the power, 2016-11-29 08:51:08]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[kojii, 2016-11-29 09:27:01]

lgtm

[commit-bot: I haz the power, 2016-11-29 10:20:27]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1480409451005820, "parent_rev":
"c51e3f6566b191e0c4662f699cf8f0b099874374", "commit_rev":
"efd5d636109c99727c6b0cbc264cd5b947706cbc"}

[commit-bot: I haz the power, 2016-11-29 10:20:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-11-29 10:22:53]

Description was changed from

==========
Improve fallback for Burmese with leading punctuation + spacing mark

Reland after revert in 1b8f4236e2dbf4e07bf0171300003168633b8660,
previous CL https://codereview.chromium.org/2530153002/
Previously failing Win10 test needs a rebaseline.

Issue 618178 describes an example where a Burmese text run starts with a
leading punctuation character followed by a combining spacing mark. This
grapheme cannot be shaped with the default font, since Times for example
cannot display the combination of a left quote with a Burmese combining
mark. Our fallback code attempts to find a fallback font based on the
first character at the beginning of an extracted unshaped sub-run, which
does not lead to finding a font suitable for Myanmar text in this case.
So in a way it runs into a fallback trap, where no fallback hint helps
to find the right fallback font and the whole run ends up as notdef
glyphs.

This CL attempts to resolve this by looking for a better fallback hint
character, which is not script common or inherited, if such is
available. This improves the situation for the Burmese text from the
issue report.

In addition, as a better fix we should give higher importance to the
locale information in font fallback, filed as issue 668706.

BUG=618178
TBR=eae,kojii,behdad
==========

to

==========
Improve fallback for Burmese with leading punctuation + spacing mark

Reland after revert in 1b8f4236e2dbf4e07bf0171300003168633b8660,
previous CL https://codereview.chromium.org/2530153002/
Previously failing Win10 test needs a rebaseline.

Issue 618178 describes an example where a Burmese text run starts with a
leading punctuation character followed by a combining spacing mark. This
grapheme cannot be shaped with the default font, since Times for example
cannot display the combination of a left quote with a Burmese combining
mark. Our fallback code attempts to find a fallback font based on the
first character at the beginning of an extracted unshaped sub-run, which
does not lead to finding a font suitable for Myanmar text in this case.
So in a way it runs into a fallback trap, where no fallback hint helps
to find the right fallback font and the whole run ends up as notdef
glyphs.

This CL attempts to resolve this by looking for a better fallback hint
character, which is not script common or inherited, if such is
available. This improves the situation for the Burmese text from the
issue report.

In addition, as a better fix we should give higher importance to the
locale information in font fallback, filed as issue 668706.

BUG=618178
TBR=eae,kojii,behdad

Committed: https://crrev.com/04f5eaaa234b142614e315f3ccd94f4e55015f10
Cr-Commit-Position: refs/heads/master@{#434944}
==========

[commit-bot: I haz the power, 2016-11-29 10:22:54]

Patchset 1 (id:??) landed as
https://crrev.com/04f5eaaa234b142614e315f3ccd94f4e55015f10
Cr-Commit-Position: refs/heads/master@{#434944}