src/vs/workbench/api/common/extHostExtensionActivator.ts/ExtensionsActivator/activateByEvent
class ExtensionsActivator:	public activateByEvent(activationEvent: string, startup: boolean): Promise<void> {
		if (this._alreadyActivatedEvents[activationEvent]) {
			return NO_OP_VOID_PROMISE;
		}
		const activateExtensions = this._registry.getExtensionDescriptionsForActivationEvent(activationEvent);
		return this._activateExtensions(activateExtensions.map(e => ({
			id: e.identifier,
			reason: { startup, extensionId: e.identifier, activationEvent }
		}))).then(() => {
			this._alreadyActivatedEvents[activationEvent] = true;
		});
	}