mat-toolbar does not display correctly on Safari, iOS simulator and Android emulator

#### Bug, feature request, or proposal:
- [x] Bug

#### What is the expected behavior?
`mat-toolbar` display correctly on all (recent) desktop and mobile browsers.

#### What is the current behavior?
`mat-toolbar` does not display correctly on Safari, iOS simulator and Android emulator.
Works fine on Chrome and real Android devices (using Chrome webview).

Safari shows the issue here, but the behavior is the same on android/ios simulator webview.

#### What are the steps to reproduce?
1. clone this repo: https://github.com/ngx-rocket/starter-kit/tree/pwa/material
2. `git checkout pwa/material`
3. `npm install`
4. `npm start` and load the website on safari

I tried to reproduce a simpler case on StackBlitz but could not find a productible minimal setup.
I'm also investigating if it's somehow related to the inclusion of `@angular/flex-layout`

#### What is the use-case or motivation for changing an existing behavior?
Not really usable as it is :)

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
```
@angular/cdk: 5.0.4
@angular/cli: 1.5.5
@angular/flex-layout: 2.0.0-beta.10-4905443
@angular/material: 5.0.4
@angular/service-worker: 1.0.0-beta.16
@angular-devkit/build-optimizer: 0.0.38
@angular-devkit/core: 0.0.25
@angular-devkit/schematics: 0.0.48
@ngtools/json-schema: 1.1.0
@ngtools/webpack: 1.8.5
@schematics/angular: 0.1.13
typescript: 2.4.2
webpack: 3.8.1
```
tested with safari 11.02, nexus 6/android 7 android emulator and ios 11.2 simulator.

Note that the provided repo use an older angular-material rc.2 version, but the issue is the same with the latest current version shown here I took the screenshot with.

#### Is there anything else we should know?

Reproduce the issue with the ngx-rocket starter-kit pwa/material branch by running npm install and npm start, then load it in Safari and the listed simulator webviews. Inspect mat-toolbar and the reported @angular/flex-layout interaction, since no minimal reproduction or project file is identified. Done means mat-toolbar displays correctly in the affected browsers while continuing to work in Chrome and on real Android devices.

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