perf(material/tooltip): Tiny but measurable optimization to MatToolti…

…p construction. Defer hooking up to directionality changes until overlay is created.

src/material/tooltip/tooltip.ts

@@ -220,6 +220,7 @@ export class MatTooltip implements OnDestroy, AfterViewInit {
   private _currentPosition: TooltipPosition;
   private readonly _cssClassPrefix: string = 'mat-mdc';
   private _ariaDescriptionPending: boolean;
+  private _dirSubscribed = false;
 
   /** Allows the user to define the position of the tooltip relative to the parent element */
   @Input('matTooltipPosition')
@@ -395,12 +396,6 @@ export class MatTooltip implements OnDestroy, AfterViewInit {
       }
     }
 
-    this._dir.change.pipe(takeUntil(this._destroyed)).subscribe(() => {
-      if (this._overlayRef) {
-        this._updatePosition(this._overlayRef);
-      }
-    });
-
     this._viewportMargin = MIN_VIEWPORT_TOOLTIP_THRESHOLD;
   }
 
@@ -567,6 +562,15 @@ export class MatTooltip implements OnDestroy, AfterViewInit {
       this._overlayRef.addPanelClass(`${this._cssClassPrefix}-tooltip-panel-non-interactive`);
     }
 
+    if (!this._dirSubscribed) {
+      this._dirSubscribed = true;
+      this._dir.change.pipe(takeUntil(this._destroyed)).subscribe(() => {
+        if (this._overlayRef) {
+          this._updatePosition(this._overlayRef);
+        }
+      });
+    }
+
     return this._overlayRef;
   }