Adds ability to add plugins to precaching lifecycle

[gauntface]

R: @jeffposnick

This adds plugins to precaching so a developer could add in the broadcast cache update behavior if they want it.

workbox.precaching.addPlugins([
    new workbox.broadcastUpdate.Plugin({ channelName: 'example-channel' })
]);

[jeffposnick]

LGTM with the one string change.

[jeffposnick]

suppressWarnings => addPlugins

[coveralls]

Changes Unknown when pulling aeb3cfd on precache-plugins into ** on v3**.

[workbox-pr-bot]

PR-Bot Size Plugin

Changed File Sizes

File	Before	After	Change	GZipped
packages/workbox-precaching/build/workbox-precaching.prod.js	4.86 KB	4.93 KB	+1%	1.93 KB

New Files

No new files have been added.

All File Sizes

View Table

File	Before	After	Change	GZipped
packages/workbox-background-sync/build/workbox-background-sync.prod.js	3.17 KB	3.17 KB	0%	1.34 KB
packages/workbox-broadcast-cache-update/build/workbox-broadcast-cache-update.prod.js	1.05 KB	1.05 KB	0%	565 B
packages/workbox-build/build/_types.js	41 B	41 B	0%	61 B
packages/workbox-build/build/index.js	2.52 KB	2.52 KB	0%	1.06 KB
packages/workbox-cache-expiration/build/workbox-cache-expiration.prod.js	3.25 KB	3.25 KB	0%	1.20 KB
packages/workbox-cacheable-response/build/workbox-cacheable-response.prod.js	593 B	593 B	0%	343 B
packages/workbox-cli/build/app.js	4.57 KB	4.57 KB	0%	1.65 KB
packages/workbox-cli/build/bin.js	2.53 KB	2.53 KB	0%	1.07 KB
packages/workbox-core/build/workbox-core.prod.js	6.67 KB	6.67 KB	0%	2.61 KB
packages/workbox-google-analytics/build/workbox-google-analytics.prod.js	1.94 KB	1.94 KB	0%	985 B
packages/workbox-precaching/build/workbox-precaching.prod.js	4.86 KB	4.93 KB	+1%	1.93 KB
packages/workbox-range-requests/build/workbox-range-requests.prod.js	1.66 KB	1.66 KB	0%	817 B
packages/workbox-routing/build/workbox-routing.prod.js	2.74 KB	2.74 KB	0%	1.23 KB
packages/workbox-strategies/build/workbox-strategies.prod.js	3.22 KB	3.22 KB	0%	1.00 KB
packages/workbox-sw/build/workbox-sw.js	1.46 KB	1.46 KB	0%	792 B
packages/workbox-webpack-plugin/build/index.js	7.29 KB	7.29 KB	0%	2.45 KB

Workbox Aggregate Size Plugin

☠️ WARNING ☠️

We are using 152% of our max size budget.

Total Size: 22.32KB
Percentage of Size Used: 152%

Gzipped: 8.89KB

[coveralls]

Changes Unknown when pulling 3f21d85 on precache-plugins into ** on v3**.