fix(tooltip): panel element blocks hover effects

By default the overlay container always has pointer events disabled. Currently the tooltip component also has pointer events disabled. The only thing that has pointer events enabled is the overlay panel element.

This can be problematic because as soon as someone hovers of the overlay panel element, the pointer events & hover effects are going to the overlay panel element instead of the element that the tooltip just overlays.

Fixes #4691

src/lib/tooltip/tooltip.scss

@@ -5,8 +5,11 @@ $mat-tooltip-horizontal-padding: 8px;
 $mat-tooltip-max-width: 250px;
 $mat-tooltip-margin: 14px;
 
-:host {
-  pointer-events: none;
+.mat-tooltip-panel {
+  // The overlay reference updates the pointer-events style property directly on the HTMLElement
+  // depending on the state of the overlay. For tooltips the overlay panel should never enable
+  // pointer events. To overwrite the inline CSS from the overlay reference `!important` is needed.
+  pointer-events: none !important;
 }
 
 .mat-tooltip {

src/lib/tooltip/tooltip.spec.ts

@@ -12,16 +12,21 @@ import {
   ViewChild,
   ChangeDetectionStrategy
 } from '@angular/core';
+import {
+  TooltipPosition,
+  MdTooltip,
+  MdTooltipModule,
+  SCROLL_THROTTLE_MS,
+  TOOLTIP_PANEL_CLASS
+} from './index';
 import {AnimationEvent} from '@angular/animations';
 import {By} from '@angular/platform-browser';
 import {NoopAnimationsModule} from '@angular/platform-browser/animations';
-import {TooltipPosition, MdTooltip, MdTooltipModule, SCROLL_THROTTLE_MS} from './index';
 import {Directionality, Direction} from '../core/bidi/index';
 import {OverlayModule, Scrollable, OverlayContainer} from '../core/overlay/index';
 import {Platform} from '../core/platform/platform';
 import {dispatchFakeEvent} from '@angular/cdk/testing';
 
-
 const initialTooltipMessage = 'initial tooltip message';
 
 describe('MdTooltip', () => {
@@ -115,6 +120,18 @@ describe('MdTooltip', () => {
       expect(overlayContainerElement.textContent).toContain(initialTooltipMessage);
     }));
 
+    it('should set a css class on the overlay panel element', fakeAsync(() => {
+      tooltipDirective.show();
+      fixture.detectChanges();
+      tick(0);
+
+      const overlayRef = tooltipDirective._overlayRef;
+
+      expect(overlayRef).not.toBeNull();
+      expect(overlayRef!.overlayElement.classList).toContain(TOOLTIP_PANEL_CLASS,
+          'Expected the overlay panel element to have the tooltip panel class set.');
+    }));
+
     it('should not show if disabled', fakeAsync(() => {
       // Test that disabling the tooltip will not set the tooltip visible
       tooltipDirective.disabled = true;

src/lib/tooltip/tooltip.ts

@@ -52,6 +52,9 @@ export const TOUCHEND_HIDE_DELAY = 1500;
 /** Time in ms to throttle repositioning after scroll events. */
 export const SCROLL_THROTTLE_MS = 20;
 
+/** CSS class that will be attached to the overlay panel. */
+export const TOOLTIP_PANEL_CLASS = 'mat-tooltip-panel';
+
 /** Creates an error to be thrown if the user supplied an invalid tooltip position. */
 export function getMdTooltipInvalidPositionError(position: string) {
   return Error(`Tooltip position "${position}" is invalid.`);
@@ -275,6 +278,7 @@ export class MdTooltip implements OnDestroy {
 
     config.direction = this._dir ? this._dir.value : 'ltr';
     config.positionStrategy = strategy;
+    config.panelClass = TOOLTIP_PANEL_CLASS;
     config.scrollStrategy = this._overlay.scrollStrategies.reposition({
       scrollThrottle: SCROLL_THROTTLE_MS
     });