Add y-axis tick labels.

This is intended to by used for visualizing catagorical data, i.e. mapping
numerical enum values to string labels.

Bug: webrtc:10623
Change-Id: Ic9c3da9a3874f479c07412f394a774ae90fd3d7e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/145408
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Commit-Queue: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28656}

rtc_tools/event_log_visualizer/plot_base.cc

@@ -66,6 +66,11 @@ void Plot::SetSuggestedYAxis(float min_value,
   SetYAxis(min_value, max_value, label, bottom_margin, top_margin);
 }
 
+void Plot::SetYAxisTickLabels(
+    const std::vector<std::pair<float, std::string>>& labels) {
+  yaxis_tick_labels_ = labels;
+}
+
 void Plot::SetTitle(const std::string& title) {
   title_ = title;
 }