Reorder the definitions in chrome_url_request_context.cc to match the declaration order.

This is strictly a no-op refactor, it does not change any code (just re-orders it within the file).
This addresses a TODO to tidy the code.

TBR=darin
TEST=none
BUG=none

Review URL: http://codereview.chromium.org/360030

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@31040 0039d316-1c4b-4281-b951-d872f2087c98