Reorder and group method declarations and add one comment for readability
Reorder and group method declarations and add one comment for readability

responseType related methods are reordered so that accessor goes first
to be consistent with the other methods.

Added a comment about internalAbort() explaining that the method may
trigger V8 GC.

BUG=none

Review URL: https://codereview.chromium.org/667203003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@184143 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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