Perform profile file analysis in dex2oat

Dex2oat can accept now multiple profile files to drive a profile based
compilation. --profile-file and --reference-profile-file speficy a pair
of profile files which will be evaluated for significant differences
before starting the compilation. If the difference is insignificant
(according to some internal metric) the compilation is skipped and a
message is logged.

Multiple pairs of --profile-file and --reference-profile-file can be
specified. This effectively enables multi user support since profiles
for different users will be kept separately.

--reference-profile-file can be left out, case in which the decision is
solely based on --profile-file. If both flags are present, then their
repetition should form unique pairs.

If the compilation is performed and --reference-profile-file is given
then its data is merged with the data from the corresponding --profile-
file and saved back to the file.

If no profile flags are given, dex2oat proceeds as before and compiles
the dex files unconditionally.

As part of this change
- merge ProfileCompilationInfo and OfflineProfilingInfo under the same
object. There was no use to keep them separate anymore.
- SaveProfilingInfo now merges the data with what was in
the file before instead of overwriting it.

Bug: 26080105

Change-Id: Ia8c8b55587d468bca5179f78941854285426234d