Implement interface for using web plotter from C++

It's not actually usable yet due to ODR violations created by
abseil being compiled into libwebrtc_full.a, but it does work based
on testing I've done with using websockets for data transfer.

Change-Id: I574570c7b5c85df9e53321bfb971a608d20b9803
diff --git a/frc971/analysis/plot_index.ts b/frc971/analysis/plot_index.ts
index 8fbdb7c..6b0e0e2 100644
--- a/frc971/analysis/plot_index.ts
+++ b/frc971/analysis/plot_index.ts
@@ -24,6 +24,7 @@
 import * as proxy from 'org_frc971/aos/network/www/proxy';
 import {plotImu} from 'org_frc971/frc971/wpilib/imu_plotter';
 import {plotDemo} from 'org_frc971/aos/network/www/demo_plot';
+import {plotData} from 'org_frc971/frc971/analysis/plot_data_utils';
 
 import Connection = proxy.Connection;
 import Configuration = configuration.aos.Configuration;
@@ -77,7 +78,8 @@
 // presence of certain channels.
 const plotIndex = new Map<string, PlotState>([
   ['Demo', new PlotState(plotDiv, plotDemo)],
-  ['IMU', new PlotState(plotDiv, plotImu)]
+  ['IMU', new PlotState(plotDiv, plotImu)],
+  ['C++ Plotter', new PlotState(plotDiv, plotData)],
 ]);
 
 const invalidSelectValue = 'null';