perf evsel: Subclassing

Provide a method to be called at tool start to config the perf_evsel
instance size, together with optional constructor and destructor.

This will be used so that perf_evsel doesn't always include a struct
hists, tools that works with hists/hist_entries, like report, top and
annotate, will, at start, tell the evsel class the size they need per
instance.

v2: Don't use exit as a name of a member of function parameter, as this
    breaks the build on at least fedora14 and rhel6.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-7t8cay0ieryox4gqosie85ek@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.h

@@ -112,6 +112,10 @@ struct thread_map;
 struct perf_evlist;
 struct record_opts;
 
+int perf_evsel__object_config(size_t object_size,
+			      int (*init)(struct perf_evsel *evsel),
+			      void (*fini)(struct perf_evsel *evsel));
+
 struct perf_evsel *perf_evsel__new_idx(struct perf_event_attr *attr, int idx);
 
 static inline struct perf_evsel *perf_evsel__new(struct perf_event_attr *attr)