Further limit the number of extra pids dumped as this is expensive.

In addition to being expensive, it can delay the thread dump of consecutive ANRs which will make the thread dumps less accurate.

The top 2 processes should be enough to debug the ANR.

Change-Id: I1a10c4e8501d705dcc1b36190db53d334f773b23
Bug: 254634348
Test: unit tests