GitLab

In test runner: Removed logic using xctest path existence to decide
whether to run as xctest.

In test configs:
Added xctest test arg to all iOS tests in chromium. This will be
required for all unit tests. Also add this to EG2 tests for consistency
of argument meaning for iOS test runner scripts.
Comparing test configs in json files, this change:
- Added the flag to all tests ToTiOSDevice, ToTiOS, ios-simulator-cronet
who didn't have this flag in any tests but were building with .xctest.
- Added to all EG2 test targets on rest of iOS builders running tests.

We have the option to build xctest arg into test runner wrapper in gn,
but it's preferred to set at test configs for fine-grained control.

Bug: 1085603, 1006881, 1085603，1001667
Change-Id: I46d7c1995ed9f9f5d96fe0280124767360f0aa21
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2413298Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Zhaoyang Li <zhaoyangli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814876}