Support "shouldResetAppCache" request parameter.
This patch pulls parameter value to AppCacheRequestHandler.
When parameter value is true - cache corresponding to manifest_url is resetted.
shouldResetAppCache parameter is set by DevTools when "Disable Cache" mode is on, to ensure that pages are reloaded from network.
Blink patch: https://codereview.chromium.org/
723113002
BUG=256672
Committed: https://crrev.com/
fd1ed6c36a08666dea471546c6e63d92997e815f
Cr-Commit-Position: refs/heads/master@{#305795}
Review URL: https://codereview.chromium.org/
669133002
Cr-Commit-Position: refs/heads/master@{#305960}