[Autofill] Fix HasPrediction() matcher

MATCHER_P should return a boolean that indicates success or failure and
not use EXPECT_* themselves.

This CL changes the matcher accordingly and uses a simple function
instead.

Bug: 40100455
Change-Id: I9bd50e840482b39c4f1b02714c75bb42d3a7bf36
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5967094
Commit-Queue: Jihad Hanna <jihadghanna@google.com>
Auto-Submit: Christoph Schwering <schwering@google.com>
Reviewed-by: Jihad Hanna <jihadghanna@google.com>
Cr-Commit-Position: refs/heads/main@{#1374318}