Followup WorkerModuleFetchCoordinater, move test code to shared file

Both the new and old code use an identical ClientImpl test class.
In jumbo builds those end up in the same translation unit and
it won't compile. This patch moves the class to a shared file
WorkerFetchTestHelper.h

Bug: 680046
Change-Id: Iabe58f2f2c93e4d77fb36c8c454952af994d302c
Reviewed-on: https://chromium-review.googlesource.com/968363
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544077}
4 files changed