This CL is a precursor to allowing shared writing to fix cache lock.

This CL allows transactions to continue to their validation phase even when another
transaction is the active reader/writer. After the validation phase, if its a match
the transaction might wait till the response is written to the cache by the active
writer. If its not a match the transaction will doom the entry and go to the
network. In a subsequent CL, the not matching case will create a new entry as well.

BUG=472740, 715913, 715974, 715920, 715911, 713348

Review-Url: https://codereview.chromium.org/2721933002
Cr-Original-Commit-Position: refs/heads/master@{#467426}
Committed: https://chromium.googlesource.com/chromium/src/+/1e2e347f957ef889aaee527bb757849f76e8a808
Review-Url: https://codereview.chromium.org/2721933002
Cr-Commit-Position: refs/heads/master@{#479204}
13 files changed