ui: Center 'Loading...' text when checkerboarding am: 501a9ac7a5 am: 2f2f37aa7b
ui: Center 'Loading...' text when checkerboarding am: 501a9ac7a5 am: 2f2f37aa7b

Original change: https://android-review.googlesource.com/c/platform/external/perfetto/+/1835213

Change-Id: I1b7fef6bcadeba3d9a5f7c4c0cb51277a017c344

google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto