Cache gfx::RenderText instances in views::Label.

[ REVIVED AS https://codereview.chromium.org/867003002/ ]

Cache gfx::RenderText instances in views::Label.

Cache RenderText instances, avoid Canvas::DrawString*. 
(avoids repeating itemization, layout, etc. on each paint) 
Recalculate colors and reset the layout as needed. 
Large cleanup; remove obsolete flag tests; update tests. 

Update App List's CachedLabel views::Label subclass use. 
(SchedulePaintInRect triggered paint with color changes) 
Ensure SetTitleSubpixelAA is otherwise called as needed. 
(skip early return; which breaks folder reorganization) 

BUG=240037, 125348
TEST=Improved Browser UI text rendering performance (especially for RTL tab title dragging), no appearance changes.
R=sky@chromium.org

[ckocagil, 2014-12-16 15:37:15]

+vadimt: Perhaps this CL fixes the text rendering perf issues.
http://crbug.com/431326

[Daniel Erat, 2014-12-16 15:52:52]

On 2014/12/16 15:37:15, ckocagil wrote:
> +vadimt: Perhaps this CL fixes the text rendering perf issues.
> http://crbug.com/431326

if this change ever comes back to life and goes in, it'll make me happy since it
seems to inadvertently fix a bug that's blocking my fix for
http://crbug.com/370226. :-) (i have zero window chops and don't understand the
full implications of it, although i'm happy to deal with any linux or chrome os
issues.)

[ckocagil, 2015-01-07 14:09:04]

Without this patch, we're doing full RenderText shaping(s) for every
|Label::OnPaint| for text eliding!!

Mike, does this CL need much work? Can we land this for M-41 before it branches
for beta? Otherwise I'll consider caching CalculateDrawStringParams results for
each Label until this is ready.

[msw, 2015-01-07 17:20:26]

On 2015/01/07 14:09:04, ckocagil wrote:
> Without this patch, we're doing full RenderText shaping(s) for every
> |Label::OnPaint| for text eliding!!
> 
> Mike, does this CL need much work? Can we land this for M-41 before it
branches
> for beta? Otherwise I'll consider caching CalculateDrawStringParams results
for
> each Label until this is ready.

I haven't attempted to rebase this for approximately 5 months... Feel free to
take over this CL; I felt that it was pretty close to ready back then, but
Alexei was concerned about the performance impact and I never adequately
assessed the impact or added performance testing.

[ckocagil, 2015-02-13 20:25:58]

This CL is revived as https://codereview.chromium.org/867003002/. This one can
be closed.