Remove BooleanPrefMember usage from Data Reduction Proxy IO classes.
The UI objects (specifically DataReductionProxySettings) already creates
a BooleanPrefMember for kDataReductionProxyEnabled and checks for changes
on it, then propagates this information to DataReductionProxyIOData via
DataReductionProxyIOData::SetProxyPrefs.
It also negates the need to pass a BooleanPrefMember to BypassStats when
ultimately all we care about is the boolean value.
BUG=
472290
Committed:
https://crrev.com/a0ad227fe2d8630e34c1bc7c752957b2666c01ff
Cr-Commit-Position: refs/heads/master@{#327138}