fix(menu): align appearance with spec

Aligns the menu panel appearance with [the spec](https://material.io/guidelines/components/menus.html) by:
* Reducing the elevation from 8 to 3.
* Adding a slight border radius.
* Tweaking the animation to match the examples.

Relates to angular#3814.

Author: crisbeto

src/lib/autocomplete/autocomplete.scss

@@ -13,9 +13,9 @@ $mat-autocomplete-panel-below-offset: 6px !default;
 $mat-autocomplete-panel-above-offset: -24px !default;
 
 .mat-autocomplete-panel {
-  @include mat-menu-base();
+  @include mat-menu-base(8);
   visibility: hidden;
-  
+
   max-width: none;
   max-height: $mat-autocomplete-panel-max-height;
   position: relative;

src/lib/core/style/_menu-common.scss

@@ -13,8 +13,8 @@ $mat-menu-side-padding: 16px !default;
 $mat-menu-icon-margin: 16px !default;
 
 
-@mixin mat-menu-base() {
-  @include mat-elevation(8);
+@mixin mat-menu-base($elevation) {
+  @include mat-elevation($elevation);
   min-width: $mat-menu-overlay-min-width;
   max-width: $mat-menu-overlay-max-width;
 

src/lib/menu/_menu-theme.scss

@@ -7,7 +7,7 @@
   $background: map-get($theme, background);
   $foreground: map-get($theme, foreground);
 
-  .mat-menu-content {
+  .mat-menu-panel {
     background: mat-color($background, 'card');
   }
 

src/lib/menu/menu-animations.ts

@@ -32,22 +32,23 @@ import{
 
 // TODO(kara): switch to :enter and :leave once Mobile Safari is sorted out.
 export const transformMenu: AnimationTriggerMetadata = trigger('transformMenu', [
-  state('showing', style({
+  state('void', style({
+    opacity: 0,
+    transform: 'scale(0, 0)'
+  })),
+  state('enter-start', style({
     opacity: 1,
-    transform: `scale(1)`
+    transform: `scale(1, 0.5)`
   })),
-  transition('void => *', [
-    style({
-      opacity: 0,
-      transform: `scale(0)`
-    }),
-    animate(`200ms cubic-bezier(0.25, 0.8, 0.25, 1)`)
-  ]),
-  transition('* => void', [
-    animate('50ms 100ms linear', style({opacity: 0}))
-  ])
+  state('enter', style({
+    transform: 'scale(1, 1)'
+  })),
+  transition('void => enter-start', animate('100ms linear')),
+  transition('enter-start => enter', animate('300ms cubic-bezier(0.25, 0.8, 0.25, 1)')),
+  transition('* => void', animate('150ms 50ms linear', style({opacity: 0})))
 ]);
 
+
 /**
  * This animation fades in the background color and content of the menu panel
  * after its containing element is scaled in.
@@ -56,6 +57,6 @@ export const fadeInItems: AnimationTriggerMetadata = trigger('fadeInItems', [
   state('showing', style({opacity: 1})),
   transition('void => *', [
     style({opacity: 0}),
-    animate(`200ms 100ms cubic-bezier(0.55, 0, 0.55, 0.2)`)
+    animate(`400ms 100ms cubic-bezier(0.55, 0, 0.55, 0.2)`)
   ])
 ]);

src/lib/menu/menu-directive.ts

@@ -20,6 +20,7 @@ import {
   ViewEncapsulation,
   ElementRef,
 } from '@angular/core';
+import {AnimationEvent} from '@angular/animations';
 import {MenuPositionX, MenuPositionY} from './menu-positions';
 import {throwMdMenuInvalidPositionX, throwMdMenuInvalidPositionY} from './menu-errors';
 import {MdMenuItem} from './menu-item';
@@ -53,6 +54,9 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
   /** Config object to be passed into the menu's ngClass */
   _classList: any = {};
 
+  /** Current state of the panel animation. */
+  _panelAnimationState: 'void' | 'enter-start' | 'enter' = 'void';
+
   /** Position of the menu in the X axis. */
   @Input()
   get xPosition() { return this._xPosition; }
@@ -156,4 +160,21 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
     this._classList['mat-menu-below'] = posY === 'below';
   }
 
+  /** Starts the enter animation. */
+  _startAnimation() {
+    this._panelAnimationState = 'enter-start';
+  }
+
+  /** Resets the panel animation to its initial state. */
+  _resetAnimation() {
+    this._panelAnimationState = 'void';
+  }
+
+  /** Callback that is invoked when the panel animation completes. */
+  _onAnimationDone(event: AnimationEvent) {
+    // After the initial expansion is done, trigger the second phase of the enter animation.
+    if (event.toState === 'enter-start') {
+      this._panelAnimationState = 'enter';
+    }
+  }
 }

src/lib/menu/menu-trigger.ts

@@ -33,6 +33,7 @@ import {
 } from '../core';
 import {Subscription} from 'rxjs/Subscription';
 import {MenuPositionX, MenuPositionY} from './menu-positions';
+import {MdMenu} from './menu-directive';
 
 // TODO(andrewseguin): Remove the kebab versions in favor of camelCased attribute selectors
 
@@ -110,6 +111,10 @@ export class MdMenuTrigger implements AfterViewInit, OnDestroy {
       this._createOverlay().attach(this._portal);
       this._subscribeToBackdrop();
       this._initMenu();
+
+      if (this.menu instanceof MdMenu) {
+        this.menu._startAnimation();
+      }
     }
   }
 
@@ -119,6 +124,10 @@ export class MdMenuTrigger implements AfterViewInit, OnDestroy {
       this._overlayRef.detach();
       this._backdropSubscription.unsubscribe();
       this._resetMenu();
+
+      if (this.menu instanceof MdMenu) {
+        this.menu._resetAnimation();
+      }
     }
   }
 

src/lib/menu/menu.html

@@ -1,6 +1,12 @@
 <ng-template>
-  <div class="mat-menu-panel" [ngClass]="_classList" (keydown)="_handleKeydown($event)"
-    (click)="_emitCloseEvent()" [@transformMenu]="'showing'" role="menu">
+  <div
+    class="mat-menu-panel"
+    [ngClass]="_classList"
+    (keydown)="_handleKeydown($event)"
+    (click)="_emitCloseEvent()"
+    [@transformMenu]="_panelAnimationState"
+    (@transformMenu.done)="_onAnimationDone($event)"
+    role="menu">
     <div class="mat-menu-content" [@fadeInItems]="'showing'">
       <ng-content></ng-content>
     </div>

src/lib/menu/menu.scss

@@ -7,11 +7,13 @@
 @import '../core/a11y/a11y';
 
 $mat-menu-vertical-padding: 8px !default;
+$mat-menu-border-radius: 2px !default;
 
 .mat-menu-panel {
-  @include mat-menu-base();
+  @include mat-menu-base(2);
   @include mat-menu-positions();
   max-height: calc(100vh - #{$mat-menu-item-height});
+  border-radius: $mat-menu-border-radius;
 
   @include cdk-high-contrast {
     outline: solid 1px;

src/lib/select/select.scss

@@ -118,7 +118,7 @@ $mat-select-panel-max-height: 256px !default;
 }
 
 .mat-select-panel {
-  @include mat-menu-base();
+  @include mat-menu-base(8);
   padding-top: 0;
   padding-bottom: 0;
   max-height: $mat-select-panel-max-height;