CDK BreapointObserver emits multiple 'true' for differents sizes of screen

#### Reproduction
Steps to reproduce:
1. Write this code in a service, then subscribe. See in console.
```
isLandscape$: Observable = this.breakpointObserver.observe(['(orientation: portrait)', '(orientation: landscape)']).pipe(
map((result: BreakpointState) => {
console.log('result', result);
return result.matches;
})
);
screenSizes$: Observable = this.breakpointObserver
.observe([Breakpoints.XSmall, Breakpoints.Small, Breakpoints.Medium, Breakpoints.Large, Breakpoints.XLarge])
.pipe(
map((result: BreakpointState) => {
console.log('result', result);
return result.matches;
})
);
```

#### Expected Behavior

What behavior were you expecting to see?

I'm expecting to get only 1 condition set to true for media queries defined in the CDK.

#### Actual Behavior

What behavior did you actually see?

My browser is 1903px wide. The 1st time i load the page, I see in the console the Large and XLarge conditions set to true:

```
(min-width: 1280px) and (max-width: 1919.99px): true
(min-width: 1920px): true
```
Then, when I resize my window, this time, the CDK emits only `(min-width: 1280px) and (max-width: 1919.99px): true`.

The same type of error occurs screen when I first get to 'xs' screen by resizing the window: 2 conditions set to true (for Small & XSmall screen sizes):

```
(max-width: 599.99px): true
(min-width: 600px) and (max-width: 959.99px): true
```
Then, when I resize again my window, i only get `(max-width: 599.99px): true`.

ALSO:

When i reload the page in 'xs' size, I get the right values set for both isLandscape & Screen size.
But when i resize the page, I get:
```
breakpoints: {
(orientation: landscape): false
(orientation: portrait): false
}
matches: false
```
I also get a no match from times to times for the screen sizes...

So, that's just not possible.
- The CDK should be able to emit that I'm still in portrait mode,
- the CDK should be able to detect my screen size any time.

#### Environment

- Angular: 8.0.0
- CDK/Material: 8.0.0
- Browser(s): Chrome 76
- Operating System (e.g. Windows, macOS, Ubuntu): Windows 10

Commencez par l’utilisation de BreakpointObserver présentée dans la reproduction et exécutez-la avec les tailles de viewport signalées dans Angular 8. Comparez les émissions initiales et celles produites lors du redimensionnement pour les requêtes d’orientation et de taille d’écran. C’est terminé lorsque chaque viewport signale systématiquement les bonnes conditions correspondantes, sans résultats dupliqués transitoires ni résultats sans correspondance.

Rédigé par le modèle d'indexation à partir du texte de l'issue.