Fix int16_t for glyphs, const glyphs, and clarify glyph loop.

Several places in the PDF code are using int16_t for glyphs. With
newer NotoSans fonts, all possible glyph ids are being used, so this
can lead to problems.

The PDF glyphs from text code returns the text for the glyphs if the
encoding is for glyphs. However, it returns this using an unsafe const
cast which is hiding possible bugs and preventing correct use of const
in other places.

The way the glyph loop in SkPDFDevice::drawPosText is written uses a
'--i' in the loop, which makes it appear this can loop forever. I don't
believe it can, but it is an unecessary code folding. We should also at
least assert the forward progress correctness here.

Review URL: https://codereview.chromium.org/626613002

Cherry-pick: 22edc83
Approval: https://code.google.com/p/chromium/issues/detail?id=418939#c30

DirectWrite to use aliased if ClearType is empty.

Some CJK fonts with some versions of DirectWrite return valid
data for bitmaps, but not for cleartype data.

For reference, two screenshots. M37 Stable and then with this patch:

https://imgur.com/9pf3rB9,EiTb6Li

See https://code.google.com/p/chromium/issues/detail?id=396624#c10 for
content of test html file.

[email protected], [email protected], [email protected], [email protected], [email protected]
BUG=chromium:407945

Review URL: https://codereview.chromium.org/504343007

DirectWrite to use aliased if ClearType is empty.

Some CJK fonts with some versions of DirectWrite return valid
data for bitmaps, but not for cleartype data.

For reference, two screenshots. M37 Stable and then with this patch:

https://imgur.com/9pf3rB9,EiTb6Li

See https://code.google.com/p/chromium/issues/detail?id=396624#c10 for
content of test html file.

[email protected], [email protected], [email protected], [email protected], [email protected]
BUG=chromium:407945

Review URL: https://codereview.chromium.org/504343007

Cherry-picked from b2f7fce.

DirectWrite to use aliased if ClearType is empty.

Some CJK fonts with some versions of DirectWrite return valid
data for bitmaps, but not for cleartype data.

For reference, two screenshots. M37 Stable and then with this patch:

https://imgur.com/9pf3rB9,EiTb6Li

See https://code.google.com/p/chromium/issues/detail?id=396624#c10 for
content of test html file.

[email protected], [email protected], [email protected], [email protected], [email protected]
BUG=chromium:407945

Review URL: https://codereview.chromium.org/504343007