perf report/top: Make 'e' visible in the help and make it toggle showing callchains

The 'e' and 'c' hotkeys were present for a long time, but not documented
in the help window, change 'e' to be a toggle so that it gets consistent
with other toggles like '+' and document it in the help window.

Keep 'c' as is for people used to it but don't document, as it is easier
to just use 'e' to show/hide all the callchains for a top level
histogram entry.

Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-pmyi5x34stlqmyu81rci94x9@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/browsers/hists.c

@@ -407,6 +407,11 @@ static bool hist_browser__selection_has_children(struct hist_browser *browser)
 	return container_of(ms, struct callchain_list, ms)->has_children;
 }
 
+static bool hist_browser__he_selection_unfolded(struct hist_browser *browser)
+{
+	return browser->he_selection ? browser->he_selection->unfolded : false;
+}
+
 static bool hist_browser__selection_unfolded(struct hist_browser *browser)
 {
 	struct hist_entry *he = browser->he_selection;
@@ -727,7 +732,7 @@ static int hist_browser__handle_hotkey(struct hist_browser *browser, bool warn_l
 		break;
 	case 'e':
 		/* Expand the selected entry. */
-		hist_browser__set_folding_selected(browser, true);
+		hist_browser__set_folding_selected(browser, !hist_browser__he_selection_unfolded(browser));
 		break;
 	case 'H':
 		browser->show_headers = !browser->show_headers;
@@ -2942,6 +2947,7 @@ static int perf_evsel__hists_browse(struct evsel *evsel, int nr_events,
 	"a             Annotate current symbol\n"			\
 	"C             Collapse all callchains\n"			\
 	"d             Zoom into current DSO\n"				\
+	"e             Expand/Collapse main entry callchains\n"	\
 	"E             Expand all callchains\n"				\
 	"F             Toggle percentage of filtered entries\n"		\
 	"H             Display column headers\n"			\