Allow heap dump requests with a FileDescriptor arg.

Part of a larger change to allow "am" to initiate hprof heap dumps.

The original implementation wrote data to a temp file, because we
compute the second part first while doing GC work.  Now all paths
work like DDMS, writing all data to a memstream and then copying it
out to a file at the very end.

Also, fix a potential fd leak on failure in the profiling code.

Bug 2759474.

Change-Id: I0f838cbd9948a23088f08463c3008be7198d76e7
8 files changed