Re-use safe 302s and 307s in MemoryCache.

In r166327 we added redirect chains to the memory cache to fix issue
103458. However, we punted on handling 302 and 307 redirects which are
often cacheable.

This patch doesn't add all safe 302s and 307s (cache-control: public
etc...), but it does add many.

R=japhet@chromium.org,abarth@chromium.org
BUG=364288
TEST=None

Review URL: https://codereview.chromium.org/239543016

git-svn-id: svn://svn.chromium.org/blink/trunk@171871 bbb929c8-8fbe-4397-9dbb-9b2b20218538