Fix some typescript errors in //aos/network/www/...

The typescript compiler upgrade revealed these.

Change-Id: I882e6a93fe69cd45255ae7885b57467ac6cc7498
diff --git a/aos/network/www/config_handler.ts b/aos/network/www/config_handler.ts
index c554647..8670c0a 100644
--- a/aos/network/www/config_handler.ts
+++ b/aos/network/www/config_handler.ts
@@ -33,7 +33,7 @@
       this.tree_div.appendChild(channel_div);
 
       const input_el = document.createElement('input');
-      input_el.setAttribute('data-index', i);
+      input_el.setAttribute('data-index', i.toString());
       input_el.setAttribute('type', 'checkbox');
       input_el.addEventListener('click', () => this.handleChange());
       channel_div.appendChild(input_el);
@@ -62,7 +62,7 @@
         continue;
       }
       const index = toggle.getAttribute('data-index');
-      const channel = this.config.channels(index);
+      const channel = this.config.channels(Number(index));
       const namefb = builder.createString(channel.name());
       const typefb = builder.createString(channel.type());
       Channel.startChannel(builder);
diff --git a/aos/network/www/ping_handler.ts b/aos/network/www/ping_handler.ts
index 9b37d70..a7fb0d4 100644
--- a/aos/network/www/ping_handler.ts
+++ b/aos/network/www/ping_handler.ts
@@ -4,8 +4,8 @@
   const fbBuffer = new flatbuffers.ByteBuffer(data);
   const ping = aos.examples.Ping.getRootAsPing(fbBuffer);
 
-  document.getElementById('val').innerHTML = ping.value();
-  document.getElementById('time').innerHTML = ping.sendTime().low;
+  document.getElementById('val').innerHTML = ping.value().toString();
+  document.getElementById('time').innerHTML = ping.sendTime().low.toString();
 }
 
 export function SetupDom() {
diff --git a/aos/network/www/proxy.ts b/aos/network/www/proxy.ts
index 29f055b..ee3ad69 100644
--- a/aos/network/www/proxy.ts
+++ b/aos/network/www/proxy.ts
@@ -11,7 +11,7 @@
   constructor(
       private readonly handlerFunc:
           (data: Uint8Array, sentTime: number) => void,
-      private readonly channel: RTCPeerConnection) {
+      private readonly channel: RTCDataChannel) {
     channel.addEventListener('message', (e) => this.handleMessage(e));
   }
 
@@ -49,7 +49,7 @@
 export class Connection {
   private webSocketConnection: WebSocket|null = null;
   private rtcPeerConnection: RTCPeerConnection|null = null;
-  private dataChannel: DataChannel|null = null;
+  private dataChannel: RTCDataChannel|null = null;
   private webSocketUrl: string;
 
   private configInternal: aos.Configuration|null = null;
@@ -88,7 +88,7 @@
   }
 
   getConfig() {
-    return this.config_internal;
+    return this.configInternal;
   }
 
   // Handle messages on the DataChannel. Handles the Configuration message as
@@ -128,7 +128,7 @@
   }
 
   // Called for new SDPs. Make sure to set it locally and remotely.
-  onOfferCreated(description: RTCSessionDescription): void {
+  onOfferCreated(description: RTCSessionDescriptionInit): void {
     this.rtcPeerConnection.setLocalDescription(description);
     const builder = new flatbuffers.Builder(512);
     const offerString = builder.createString(description.sdp);
@@ -151,7 +151,8 @@
     this.dataChannel = this.rtcPeerConnection.createDataChannel('signalling');
     this.handlers.add(
         new Handler((data) => this.onConfigMessage(data), this.dataChannel));
-    window.dc = this.dataChannel;
+    // TODO(james): Is this used? Can we delete it?
+    // window.dc = this.dataChannel;
     this.rtcPeerConnection.addEventListener(
         'icecandidate', (e) => this.onIceCandidate(e));
     this.rtcPeerConnection.createOffer().then(
diff --git a/aos/network/www/reflection.ts b/aos/network/www/reflection.ts
index 62cfa61..a2fe3e4 100644
--- a/aos/network/www/reflection.ts
+++ b/aos/network/www/reflection.ts
@@ -150,7 +150,7 @@
       case reflection.BaseType.Double:
         return this.bb.readFloat64(offset);
     }
-    throw new Error('Unsupported message type ' + baseType);
+    throw new Error('Unsupported message type ' + fieldType);
   }
 };
 
@@ -239,8 +239,7 @@
         return field;
       }
     }
-    throw new Error(
-        'Couldn\'t find field ' + fieldName + ' options are ' + fields);
+    throw new Error('Couldn\'t find field ' + fieldName + '.');
   }
 
   // Reads a scalar with the given field name from a Table. If readDefaults