Support float widths in RenderTextHarfBuzz.

Support float widths in RenderTextHarfBuzz.

The gfx_unittests CanvasTestMac.* passes on Mac Views.
(can also run the tests with --enable-harfbuzz-rendertext)

BUG=391843
TEST=CanvasTestMac.* passes, no Mac text rendering changes.
R=asvitkine@chromium.org,ckocagil@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=288255

[msw, 2014-08-07 20:20:37]

Hey Cem and Alexei, please take a look; thanks!

[Alexei Svitkine (slow), 2014-08-07 20:52:29]

This change LGTM I think it's the right direction for RenderText.


However, I don't think this is enough to ensure things don't break if we replace
RenderTextMac with RenderTextHarfBuzz for mainline build. I suspect for i18n
text, a test like StringSizeIdenticalForSkia would still fail (since text would
be shaped different by Harfbuzz than by CoreText). Unless HarfBuzz uses CoreText
behind the scenes on Mac?

[msw, 2014-08-07 20:53:48]

The CQ bit was checked by msw@chromium.org

[commit-bot: I haz the power, 2014-08-07 21:08:02]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/msw@chromium.org/440213004/60001

[commit-bot: I haz the power, 2014-08-08 00:59:34]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)

[commit-bot: I haz the power, 2014-08-08 08:25:27]

Change committed as 288255

[ckocagil, 2014-08-08 17:26:02]

lgtm with this comment: I'm thinking if it would be better to only use
fixed-point integers internally and only convert to float when it is needed.