[CT] Break up "isolates tests" steps into batches with <100k files for 1M run
[CT] Break up "isolates tests" steps into batches with <100k files for 1M run

BUG=skia:4944
TBR=borenet

Review URL: https://codereview.chromium.org/1692163002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@298757 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build