Fix pinpoint launching for update_wpr

Pass base_git_hash instead of start_git_hash and end_git_hash since the
API has changed:
https://chromium-review.googlesource.com/c/catapult/+/1965875

Also changes android bot from android-nexus5x-perf to
android-pixel2-perf since the latter has more capacity.

Bug: 878390
Change-Id: I6095d549f98cc613be7b0f6d6cb6ec4098e1fc7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1971840
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#725934}

tools/perf/cli_tools/update_wpr/update_wpr.py

@@ -347,8 +347,7 @@ class WprUpdater(object):
     """Creates, starts a Pinpoint job and returns its URL."""
     try:
       resp = pinpoint_service.NewJob(
-          start_git_hash='HEAD',
-          end_git_hash='HEAD',
+          base_git_hash='HEAD',
           target='performance_test_suite',
           patch=self._GetBranchIssueUrl(),
           bug_id=self.bug_id or '',
@@ -453,7 +452,7 @@ class WprUpdater(object):
       if self._IsDesktop():
         configs = ['linux-perf', 'win-10-perf', 'mac-10_12_laptop_low_end-perf']
       else:
-        configs = ['android-nexus5x-perf']
+        configs = ['android-pixel2-perf']
     for config in configs:
       job_url = self._StartPinpointJob(config)
       if not job_url:

tools/perf/cli_tools/update_wpr/update_wpr_unittest.py

@@ -368,8 +368,7 @@ class UpdateWprTest(unittest.TestCase):
         self.wpr_updater.StartPinpointJobs(),
         (['<url>', '<url>', '<url>'], []))
     new_job.assert_called_with(
-        start_git_hash='HEAD',
-        end_git_hash='HEAD',
+        base_git_hash='HEAD',
         target='performance_test_suite',
         patch='<issue-url>',
         bug_id='',
@@ -390,8 +389,7 @@ class UpdateWprTest(unittest.TestCase):
     self.assertEqual(
         self.wpr_updater.StartPinpointJobs(['<config>']), ([], ['<config>']))
     new_job.assert_called_once_with(
-        start_git_hash='HEAD',
-        end_git_hash='HEAD',
+        base_git_hash='HEAD',
         target='performance_test_suite',
         patch='<issue-url>',
         bug_id='',