Remove WebURLResponse::initialize()

The implementation of WebURLResponse::initialize() was trivial and could
easily be moved to the constructor. Remove it.

Also remove the public assign() method and the reset() method.

BUG=625529

patch from issue 2120233003 at patchset 40001 (http://crrev.com/2120233003#ps40001)

Review-Url: https://codereview.chromium.org/2117313002
Cr-Commit-Position: refs/heads/master@{#404279}
18 files changed