Un-nest configs in GN files.

People sometimes nest targets or configs, usually with the assumption that this limits the visibility of a config to within a target. But this nesting provides no visibility restrictions over declaring it outside of a block.

Un-nest for clarity.

Re-land of http://crrev.com/1318823008 while preserving config ordering.

Review URL: https://codereview.chromium.org/1307223010

Cr-Original-Commit-Position: refs/heads/master@{#346964}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6dd952c77209619a445205998173fc40fb817be1