linux: Fix text underline color/halo in Skia canvas.
linux: Fix text underline color/halo in Skia canvas.

This makes us use the correct color for underlined text and
draw a halo around the underlining when needed.

Manual testing:
- Checked that the underlining on the screen locker sign out
  link is white.
- Hacked up status area text to be underlined and checked
  that things are mostly reasonable when drawing normal,
  embossed, or haloed text.  (Actually,
  underlined-and-haloed text can get clipped in some cases,
  but I don't think that we use it anywhere and this is hard
  to fix without a lot of refactoring -- we don't specify
  whether text is going to be drawn with a halo or not when
  requesting its size.)
- Turned on underlining on tab titles and checked that the
  underline also fades out to the right on long, elided
  titles.

BUG=chromium-os:16490
TEST=manual; see above


Review URL: http://codereview.chromium.org/7466025

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@93559 0039d316-1c4b-4281-b951-d872f2087c98

adobe/chromium,gavinp/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,yitian134/chromium,ropik/chromium,yitian134/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,yitian134/chromium,yitian134/chromium,adobe/chromium,adobe/chromium,ropik/chromium,gavinp/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,ropik/chromium,yitian134/chromium,ropik/chromium,adobe/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,yitian134/chromium,gavinp/chromium,gavinp/chromium,gavinp/chromium,gavinp/chromium,adobe/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,ropik/chromium,gavinp/chromium,yitian134/chromium