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This CL allows the prefixing of category names with disabled- to have them
not traced by default. Only if an explicit disabled-foo is provided in the
category filter do we enable the category.

Providing a disabled-foo in the category filter does not act like an include
category in that all other includes have to be specified. The disables are
treated as their own group.

BUG=232109

Review URL: https://chromiumcodereview.appspot.com/14748003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@198787 0039d316-1c4b-4281-b951-d872f2087c98