Hex-escape raw UTF-8 strings in the source.

MSVC cannot deal with raw UTF-8 strings in some locales (e.g. CJK) and
the compilation will fail because UTF-8 sequences interpreted in Windows
CJK code pages will lead to 'an invalid character error'.

See http://support.microsoft.com/kb/980263 (using BOM is not acceptable
for cross-platform source files and even that is apparently broken in a
recent version of MSVC.).

TBR=abarth
BUG=304911,234797
TEST=wtf_unittests:*String*Locale

Review URL: https://codereview.chromium.org/136293005

git-svn-id: svn://svn.chromium.org/blink/trunk@165350 bbb929c8-8fbe-4397-9dbb-9b2b20218538