Prepare to use gfx::RenderText in views::Label.

Prepare to use gfx::RenderText in views::Label.

Alter Label's API to support a RenderText implementation.
This has minimal functional changes to Label for now.
The Label rewrite to use RenderText will land separately.

Remove the generally unused Label::SetDirectionalityMode.
We should always use the text's directionality anyway.
(it seems like this was the case even for *FROM_UI...)

Also remove views::LabelButton::SetDirectionalityMode.
Fix LabelButton mutli-line preferred sizing and layout.

Add RenderText flag to swap newline chars for symbols.
(We don't want that for multi-line views::Label layout)
Add GetCurrentHorizontalAlignment ALIGN_HEAD helper.
Expose ElideBehavior and ShadowValues accessors.
Set the styles of the argument FontList in SetFontList.
(this is how Label transmits style information for now)
Fix partial-pixel treatment for centered alignment.

Update Message Center's InnerBoundedLabel Label subclass.
(minimal changes to keep it working with older paint path)

BUG=240037
TEST=Negligible appearance changes (better multi-line label centering).
R=sky@chromium.org,asvitkine@chromium.org

Review URL: https://codereview.chromium.org/23228004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284401 0039d316-1c4b-4281-b951-d872f2087c98