Use QUIC for DataReductionProxy if user belongs to field trial group that starts with "Enabled".

Currently, QUIC is used if the field trial group is exactly
"Enabled". This change allows us to have multiple Enabled
groups (e.g., "Enabled", "Enabled2" etc.).

BUG=533703

Review URL: https://codereview.chromium.org/1354283002

Cr-Commit-Position: refs/heads/master@{#350061}
(cherry picked from commit 5cc3f0a27b1c73102bfeee73d6fe24e3400de633)

Review URL: https://codereview.chromium.org/1360903002 .

Cr-Commit-Position: refs/branch-heads/2490@{#356}
Cr-Branched-From: 7790a3535f2a81a03685eca31a32cf69ae0c114f-refs/heads/master@{#344925}