src/vs/platform/markers/common/markerService.ts/DoubleResourceMap/set
class DoubleResourceMap:	set(resource: URI, owner: string, value: V) {
		let ownerMap = this._byResource.get(resource);
		if (!ownerMap) {
			ownerMap = new Map();
			this._byResource.set(resource, ownerMap);
		}
		ownerMap.set(owner, value);

		let resourceMap = this._byOwner.get(owner);
		if (!resourceMap) {
			resourceMap = new ResourceMap();
			this._byOwner.set(owner, resourceMap);
		}
		resourceMap.set(resource, value);
	}