Revert 113606 - Improve RenderTextWin font fallback.

Revert 113606 - Improve RenderTextWin font fallback.

Don't use SCRIPT_UNDEFINED in the case of font fallback,
unless font fallback actually fails to return a script
that can display the characters. This fixes the problem
of some scripts not being properly displayed.

This actually makes RenderTextWin properly validate whether
a text position accepts a cursor, which caused several tests
to fail and revealed some additional issues in RenderTextWin.

The CL includes some modifications to address this.

Some tests are disabled under XP, see:
http://crbug.com/106450

Also, fixes some lint warnings.

BUG=90426
TEST=Run chrome.exe --use-pure-views and paste some Bengali
text into the omnibox. It should show up properly.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=113075
Review URL: http://codereview.chromium.org/8575020

TBR=asvitkine@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=113613