WebURLLoaderMock: do not call DidReceiveResponse on failures

The real url loader does not notify about response if it failed
before receiving first byte of the body data.

Our current of calling DidReceiveResponse before DidFail without
a single byte of data disagrees with navigation flow, which never
sends a response if failed before receiving the body.

This patch unblocks synchronous navigation commit from
DidReceiveResponse, as opposite to DidReceiveData.

Bug: 855189
Change-Id: I48691bc21a5886d3b24e14b5c1d3e2df6e36bb33
Reviewed-on: https://chromium-review.googlesource.com/c/1368653
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615252}
2 files changed