[Metadata][AIF] Log histogram on every fetch attempt

In crrev.com/c/6000395, logic was introduced to log image fetcher
histograms only once per browser session even if there were multiple
attempts. At that point in time, there were multiple triggers (8 to 9)
for image fetching on browser startup, so the metrics were getting
negatively biased. This is no more the case. There's only 1 trigger for
image fetching now.

Log histograms once for each attempt at image fetching. This also
ensures feature parity with Android.

Bug: 40276036
Change-Id: Ibf480d483f88859885b895c6a184fb4e98edcd7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6472261
Reviewed-by: Timofey Chudakov <tchudakov@google.com>
Commit-Queue: Timofey Chudakov <tchudakov@google.com>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1452696}