Use GetNormalizedValue() to retrieve Expect-CT header value

Due to a shameful test coverage oversight on my part :( Expect-CT headers
weren't being enumerated properly. Because the syntax is comma-separated
directives, EnumerateHeader() was returning only the first directive.
This change uses GetNormalizedValue() to retrieve the header value instead.
This returns the full list of comma-separated directives, and it also
combines multiple header values into one as the spec intends, such that
Expect-CT: max-age=100
Expect-CT: enforce
is treated identically to
Expect-CT: max-age=100,enforce.

Bug: 752358
Change-Id: I6b8dd78c706925a1367e9978e3986e3c29ccbd46
Reviewed-on: https://chromium-review.googlesource.com/601441
Reviewed-by: Matt Mueller <[email protected]>
Commit-Queue: Emily Stark <[email protected]>
Cr-Commit-Position: refs/heads/master@{#492484}
10 files changed