first cut at runtime skia global settings

This allows passing in a string to set runtime global information like the font cache size. I tested this by launching a modified Chromium with:

  --skia-flags='font-cache-limit=12345678'

which passed "font-cache-limit=12345678" to SkGraphics::SetFlags (without quotes).

This syntax can be extended to include more name/value pairs, separated by a semicolon.

The companion Chromium change might look like:
http://codereview.chromium.org/8561023

[caryclark1, 2011-11-18 19:54:59]

just a first cut -- happy to iterate to make more general/useful/safer

[reed1, 2011-11-18 20:05:18]

LGTM

[reed1, 2011-11-18 20:14:59]

Might add something like 

    --skia-flags='font-cache-limit=12345678'

In the header comment, to show a sample usage (or document that this is highly
volitile, and subject to format changes for now).