Query Editor Memory improvements (#3041)

* working through memory issues

* work in progress

* add missing value

* work in progress

* more work in progress

* various more memory fixes

* additional improvements

* fix imports

* change test that we dispose queries on close not dispose

* update tests

src/sql/parts/queryPlan/queryPlan.ts

@@ -15,6 +15,9 @@ import { dispose, Disposable } from 'vs/base/common/lifecycle';
 
 export class QueryPlanState {
 	xml: string;
+	dispose() {
+
+	}
 }
 
 export class QueryPlanTab implements IPanelTab {
@@ -29,6 +32,10 @@ export class QueryPlanTab implements IPanelTab {
 	public dispose() {
 		dispose(this.view);
 	}
+
+	public clear() {
+		this.view.clear();
+	}
 }
 
 export class QueryPlanView implements IPanelView {
@@ -59,6 +66,12 @@ export class QueryPlanView implements IPanelView {
 		this.container.style.height = dimension.height + 'px';
 	}
 
+	public clear() {
+		if (this.qp) {
+			this.qp.xml = undefined;
+		}
+	}
+
 	public showPlan(xml: string) {
 		if (this.qp) {
 			this.qp.xml = xml;