debug: call stack message box shows stopped reason of focused thread

fixes #1701

src/vs/workbench/parts/debug/browser/debugViewlet.ts

@@ -246,10 +246,11 @@ class CallStackView extends viewlet.CollapsibleViewletView {
 		this.toDispose.push(debugModel.addListener2(debug.ModelEvents.CALLSTACK_UPDATED, () => {
 			this.tree.refresh().done(null, errors.onUnexpectedError);
 		}));
-		this.toDispose.push(this.debugService.addListener2(debug.ServiceEvents.STATE_CHANGED, (reason: string) => {
-			if (this.debugService.getState() === debug.State.Stopped && reason !== 'step') {
-				this.messageBox.textContent = nls.localize('debugStopped', "Paused on {0}.", reason);
-				reason === 'exception' ? this.messageBox.classList.add('exception') : this.messageBox.classList.remove('exception');
+		this.toDispose.push(this.debugService.getViewModel().addListener2(debug.ViewModelEvents.FOCUSED_STACK_FRAME_UPDATED, () => {
+			const focussedThread = this.debugService.getModel().getThreads()[this.debugService.getViewModel().getFocusedThreadId()];
+			if (focussedThread && focussedThread.stoppedReason && focussedThread.stoppedReason !== 'step') {
+				this.messageBox.textContent = nls.localize('debugStopped', "Paused on {0}.", focussedThread.stoppedReason);
+				focussedThread.stoppedReason === 'exception' ? this.messageBox.classList.add('exception') : this.messageBox.classList.remove('exception');
 
 				this.messageBox.hidden = false;
 				return;

src/vs/workbench/parts/debug/common/debug.ts

@@ -128,7 +128,7 @@ export interface IViewModel extends ee.EventEmitter {
 }
 
 export interface IModel extends ee.IEventEmitter, ITreeElement {
-	getThreads(): { [reference: number]: IThread; };
+	getThreads(): { [threadId: number]: IThread; };
 	getBreakpoints(): IBreakpoint[];
 	areBreakpointsActivated(): boolean;
 	getFunctionBreakpoints(): IFunctionBreakpoint[];

src/vs/workbench/parts/debug/electron-browser/debugService.ts

@@ -228,7 +228,7 @@ export class DebugService extends ee.EventEmitter implements debug.IDebugService
 		}));
 
 		this.toDispose.push(this.session.addListener2(debug.SessionEvents.STOPPED, (event: DebugProtocol.StoppedEvent) => {
-			this.setStateAndEmit(debug.State.Stopped, event.body.reason);
+			this.setStateAndEmit(debug.State.Stopped);
 			const threadId = event.body.threadId;
 
 			this.getThreadData(threadId).then(() => {
@@ -356,9 +356,9 @@ export class DebugService extends ee.EventEmitter implements debug.IDebugService
 		return this.state;
 	}
 
-	private setStateAndEmit(newState: debug.State, data?: any): void {
+	private setStateAndEmit(newState: debug.State): void {
 		this.state = newState;
-		this.emit(debug.ServiceEvents.STATE_CHANGED, data);
+		this.emit(debug.ServiceEvents.STATE_CHANGED);
 	}
 
 	public get enabled(): boolean {