Limit gtest batch size for angle_end2end_tests

Speculative fix for flaky timeouts.
Per http://anglebug.com/4396, SwiftShader backend causes TLS descriptor
leak. Reducing the batch size stops running the tests before the OS
limit on TLS descriptor number is reached.

Side-effect:
--test-launcher-retry-limit=0
and
--test-launcher-batch-limit=256
apply now not only to desktop, but to Android as well.
Thus, using 256 as the batch limit, which is the default on Android,
in order to not introduce a regression there.

TBR=kbr

Bug: 1062692
Change-Id: I7aee19ef3765bf3cfe65417c0bf039bc59e9f6a1
No-try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2110397
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751941}

testing/buildbot/test_suites.pyl

@@ -1672,9 +1672,12 @@
       'angle_end2end_tests': {
         'desktop_args': [
           '--use-gpu-in-tests',
+        ],
+        'args': [
           # ANGLE test retries deliberately disabled to prevent flakiness.
           # http://crbug.com/669196
-          '--test-launcher-retry-limit=0'
+          '--test-launcher-retry-limit=0',
+          '--test-launcher-batch-limit=256',
         ],
         'linux_args': ['--no-xvfb'],
         'should_retry_with_patch': False,