Make all wire protocol structs stable across ABI.
Make all wire protocol structs stable across ABI.

Before this, the structs would be laid out differently on 32-bit and
64-bit ABIs. If the heapprofd service was 64-bit, but the client 32,
we would not read the structs correctly.

Bug: 163551040

Change-Id: I99d00cd40523f6b799438bfa619b9af43a51603f

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