Add a drivetrain typescript plot config

Also, add a few extra comments/error messages to other pieces of
the plotting infrastructure.

Change-Id: Iab4dded93b1c5019e6b6c3d96d66728aa2e1f2a1
diff --git a/aos/network/www/proxy.ts b/aos/network/www/proxy.ts
index 948f8db..02573b3 100644
--- a/aos/network/www/proxy.ts
+++ b/aos/network/www/proxy.ts
@@ -125,6 +125,12 @@
     const request = new ChannelRequest(channel, method);
     if (!this.handlerFuncs.has(channel.key())) {
       this.handlerFuncs.set(channel.key(), []);
+    } else {
+      if (method == TransferMethod.EVERYTHING_WITH_HISTORY) {
+        console.warn(
+            'Behavior of multiple reliable handlers is currently poorly ' +
+            'defined and may not actually deliver all of the messages.');
+      }
     }
     this.handlerFuncs.get(channel.key()).push(handler);
     this.subscribeToChannel(request);
diff --git a/aos/network/www/reflection.ts b/aos/network/www/reflection.ts
index 2e1ed8f..09206e0 100644
--- a/aos/network/www/reflection.ts
+++ b/aos/network/www/reflection.ts
@@ -246,7 +246,9 @@
         return field;
       }
     }
-    throw new Error('Couldn\'t find field ' + fieldName + '.');
+    throw new Error(
+        'Couldn\'t find field ' + fieldName + ' in object ' + schema.name() +
+        '.');
   }
 
   // Reads a scalar with the given field name from a Table. If readDefaults