src/vs/workbench/contrib/debug/common/debugModel.ts/Thread/getTopStackFrame
class Thread:	getTopStackFrame(): IStackFrame | undefined {
		const callStack = this.getCallStack();
		const firstAvailableStackFrame = callStack.find(sf => !!(sf && sf.source && sf.source.available && sf.source.presentationHint !== 'deemphasize'));
		return firstAvailableStackFrame || (callStack.length > 0 ? callStack[0] : undefined);
	}