[ui] Clean up getTrackShellButtons().

- Since `getTrackShellButtons()` now returns `m.Children`, we can
  simplify the return values in a few places.
- Also, removed getContextMenu() from TrackAdapter and
  TrackWithControllerAdapter.

Change-Id: I01669341253c8a298d8a494cea47d91a6050abdf

ui/src/common/track_adapter.ts

@@ -20,7 +20,6 @@ import {duration, Span, time} from '../base/time';
 import {EngineProxy} from '../common/engine';
 import {PxSpan, TimeScale} from '../frontend/time_scale';
 import {NewTrackArgs, SliceRect} from '../frontend/track';
-import {TrackButtonAttrs} from '../frontend/track_panel';
 
 import {BasicAsyncTrack} from './basic_async_track';
 
@@ -80,10 +79,6 @@ export class TrackWithControllerAdapter<Config, Data> extends
     return this.track.getTrackShellButtons();
   }
 
-  getContextMenu(): m.Vnode<any, {}>|null {
-    return this.track.getContextMenu();
-  }
-
   onMouseMove(position: {x: number; y: number;}): void {
     this.track.onMouseMove(position);
   }
@@ -155,14 +150,10 @@ export abstract class TrackAdapter<Config, Data> {
     return 40;
   }
 
-  getTrackShellButtons(): Array<m.Vnode<TrackButtonAttrs>> {
+  getTrackShellButtons(): m.Children {
     return [];
   }
 
-  getContextMenu(): m.Vnode<any>|null {
-    return null;
-  }
-
   onMouseMove(_position: {x: number, y: number}) {}
 
   // Returns whether the mouse click has selected something.

ui/src/frontend/base_counter_track.ts

@@ -132,9 +132,7 @@ export abstract class BaseCounterTrack<Config> extends TrackBase<Config> {
   }
 
   getTrackShellButtons(): m.Children {
-    return [
-      this.getCounterContextMenu(),
-    ];
+    return this.getCounterContextMenu();
   }
 
   renderCanvas(ctx: CanvasRenderingContext2D) {

ui/src/tracks/counter/index.ts

@@ -338,13 +338,13 @@ export class CounterTrack extends BasicAsyncTrack<Data> {
       });
     });
 
-    return [m(
+    return m(
         PopupMenu2,
         {
           trigger: m(Button, {icon: 'show_chart', minimal: true}),
         },
         menuItems,
-        )];
+    );
   }
 
   renderCanvas(ctx: CanvasRenderingContext2D): void {

ui/src/tracks/debug/slice_track.ts

@@ -79,14 +79,14 @@ export class DebugTrackV2 extends CustomSqlTableSliceTrack<DebugTrackV2Types> {
   }
 
   getTrackShellButtons(): m.Children {
-    return [m(TrackButton, {
+    return m(TrackButton, {
       action: () => {
         globals.dispatch(Actions.removeDebugTrack({trackId: this.trackId}));
       },
       i: 'close',
       tooltip: 'Close',
       showButton: true,
-    })];
+    });
   }
 }
 

ui/src/tracks/visualised_args/index.ts

@@ -17,7 +17,7 @@ import m from 'mithril';
 import {Actions} from '../../common/actions';
 import {globals} from '../../frontend/globals';
 import {NewTrackArgs, TrackBase} from '../../frontend/track';
-import {TrackButton, TrackButtonAttrs} from '../../frontend/track_panel';
+import {TrackButton} from '../../frontend/track_panel';
 import {Plugin, PluginContext, PluginDescriptor} from '../../public';
 import {
   ChromeSliceTrack,
@@ -51,17 +51,15 @@ export class VisualisedArgsTrack extends ChromeSliceTrack {
 
   getTrackShellButtons(): m.Children {
     const config = this.config as Config;
-    const buttons: Array<m.Vnode<TrackButtonAttrs>> = [];
-    buttons.push(m(TrackButton, {
+    return m(TrackButton, {
       action: () => {
         globals.dispatch(
             Actions.removeVisualisedArg({argName: config.argName}));
       },
       i: 'close',
       tooltip: 'Close',
       showButton: true,
-    }));
-    return buttons;
+    });
   }
 }