Move event cache into HTKEventBase, so it's available for all events

Author: pimterry

src/model/events/event-base.ts

@@ -38,4 +38,9 @@ export abstract class HTKEventBase {
     @observable
     public pinned: boolean = false;
 
+    // Logic elsewhere can put values into these caches to cache calculations
+    // about this event weakly, so they GC with the event.
+    // Keyed by symbols only, so we know we never have conflicts.
+    public cache = observable.map(new Map<symbol, unknown>(), { deep: false });
+
 }

src/model/http/exchange.ts

@@ -217,11 +217,6 @@ export class HttpExchange extends HTKEventBase {
         this._apiMetadataPromise = apiStore.getApi(this.request);
     }
 
-    // Logic elsewhere can put values into these caches to cache calculations
-    // about this exchange weakly, so they GC with the exchange.
-    // Keyed by symbols only, so we know we never have conflicts.
-    public cache = observable.map(new Map<symbol, unknown>(), { deep: false });
-
     public readonly request: HtkRequest;
     public readonly id: string;
 

src/model/webrtc/rtc-connection.ts

@@ -27,8 +27,6 @@ export class RTCConnection extends HTKEventBase {
 
     readonly id = this.connectionEvent.sessionId;
 
-    public readonly cache = observable.map(new Map<symbol, unknown>(), { deep: false });
-
     isRTCConnection(): this is RTCConnection  {
         return true;
     }