Report exact CSS error locations (line, column) into the console

CSSParser now tracks offsets along with lines in CSSParserLocation.
Whenever an error is to be reported (CSSParser::logError()) AND a DevTools window is open,
line endings are extracted from the stylesheet text and cached,
so that the error position offset can be converted into (line, column).

We are computing columns only when the DevTools are open, since otherwise it would regress the performance by about 1%:

tools/perf/run_measurement --browser=release blink_perf third_party/WebKit/PerformanceTests/Parser/css-parser-yui.html results:

Before:
Avg css-parser-yui: 366.230898runs/s
Sd  css-parser-yui: 0.913509runs/s

After:
Avg css-parser-yui: 362.490343runs/s
Sd  css-parser-yui: 1.114244runs/s

R=vsevik@chromium.org
BUG=257003

Review URL: https://codereview.chromium.org/18371007

git-svn-id: svn://svn.chromium.org/blink/trunk@154284 bbb929c8-8fbe-4397-9dbb-9b2b20218538