Add fade eliding for Views Labels; related cleanup.

Add fade eliding for Views Labels; related cleanup.

Support fade eliding behavior for Views Label[Button].
(needed for forthcoming LabelButton conversions, etc.)

Remove unused head fading behavior, refine fade tail.
(fades the end opposite the text's horizontal alignment)
(centered fading uses content directionality alignment)
(RenderText fades both ends of explicitly centered text)

Consolidate gfx::ElideBehavior and Label::ElideBehavior.
Nix Canvas::TruncateFadeMode and RenderText fade_[head|tail].
Add ELIDE_EMAIL and FADE_TAIL enum values, hide ElideEmail.
Consolidate and rename Canvas::DrawFadedString functions.
Refine Examples, cleanup enum and function uses.

BUG=155363, 249938
TEST=No apparent eliding behavior changes or regressions.
R=sky@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=275265

[msw, 2014-06-05 18:43:13]

Hey Scott, please take a look; thanks!

[sky, 2014-06-05 20:47:18]

LGTM

[msw, 2014-06-05 21:00:22]

The CQ bit was checked by msw@chromium.org

[commit-bot: I haz the power, 2014-06-05 21:03:46]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/msw@chromium.org/312233003/60001

[commit-bot: I haz the power, 2014-06-05 22:42:12]

Change committed as 275265