Update DOMUI pref style
Update DOMUI pref style

This makes a few small changes to bring things more in line with the latest mocks:
- Larger font size for page and section titles.
- Removes the trailing divider line after the last section.
- Tweaks the inter-section spacing.

BUG=59237,59264
TEST=DOMUI prefs should look more like mocks.

Review URL: http://codereview.chromium.org/4826002

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@65870 0039d316-1c4b-4281-b951-d872f2087c98

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