url: Add a StringPiece variant to PathForRequest

Some of the GURL methods have StringPiece variant helpers. This patch
adds a helper to GURL::PathForRequest.

Test: expands unittest
Change-Id: I488f5cf0e36861b4f7202719f3ab8997ce77c74a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900356
Reviewed-by: Charlie Harrison <[email protected]>
Commit-Queue: David Van Cleve <[email protected]>
Cr-Commit-Position: refs/heads/master@{#713007}
3 files changed