Use cache: default for precaching requests when it's safe to

[jeffposnick]

I was revisiting the changes in #2176, and realized that one unintended consequence was that if the HTTP cache contained a valid entry for a URL that could be safely read from the cache (i.e. there's no revision field for the precache manifest entry), the precaching request would still go to the network.

While this is "safe", it's less efficient.

This change accounts for that, and will set cache: 'default' for those requests that could be safely satisfied by the HTTP cache, with cache: 'reload' still being set for requests that should always ignore the cache and go against the network.

[workbox-pr-bot]

PR-Bot Size Plugin

Changed File Sizes

File	Before	After	Change	GZipped
packages/workbox-precaching/build/workbox-precaching.prod.js	4.84 KB	4.95 KB	+2%	1.92 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	3.87 KB	3.87 KB	0%	1.60 KB
packages/workbox-broadcast-update/build/workbox-broadcast-update.prod.js	1.02 KB	1.02 KB	0%	576 B
packages/workbox-build/build/_types.js	41 B	41 B	0%	61 B
packages/workbox-build/build/generate-sw.js	1.99 KB	1.99 KB	0%	966 B
packages/workbox-build/build/get-manifest.js	1.60 KB	1.60 KB	0%	779 B
packages/workbox-build/build/index.js	613 B	613 B	0%	344 B
packages/workbox-build/build/inject-manifest.js	3.13 KB	3.13 KB	0%	1.36 KB
packages/workbox-cacheable-response/build/workbox-cacheable-response.prod.js	610 B	610 B	0%	356 B
packages/workbox-cli/build/app.js	4.16 KB	4.16 KB	0%	1.64 KB
packages/workbox-cli/build/bin.js	940 B	940 B	0%	502 B
packages/workbox-core/build/workbox-core.prod.js	6.42 KB	6.42 KB	0%	2.66 KB
packages/workbox-expiration/build/workbox-expiration.prod.js	2.95 KB	2.95 KB	0%	1.27 KB
packages/workbox-google-analytics/build/workbox-offline-ga.prod.js	1.97 KB	1.97 KB	0%	915 B
packages/workbox-navigation-preload/build/workbox-navigation-preload.prod.js	659 B	659 B	0%	322 B
packages/workbox-precaching/build/workbox-precaching.prod.js	4.84 KB	4.95 KB	+2%	1.92 KB
packages/workbox-range-requests/build/workbox-range-requests.prod.js	1.58 KB	1.58 KB	0%	800 B
packages/workbox-routing/build/workbox-routing.prod.js	3.09 KB	3.09 KB	0%	1.35 KB
packages/workbox-strategies/build/workbox-strategies.prod.js	4.10 KB	4.10 KB	0%	1.13 KB
packages/workbox-streams/build/workbox-streams.prod.js	1.44 KB	1.44 KB	0%	697 B
packages/workbox-sw/build/workbox-sw.js	1.34 KB	1.34 KB	0%	746 B
packages/workbox-webpack-plugin/build/generate-sw.js	4.22 KB	4.22 KB	0%	1.61 KB
packages/workbox-webpack-plugin/build/index.js	349 B	349 B	0%	255 B
packages/workbox-webpack-plugin/build/inject-manifest.js	5.10 KB	5.10 KB	0%	1.77 KB
packages/workbox-window/build/workbox-window.dev.umd.js	41.51 KB	41.51 KB	0%	9.20 KB
packages/workbox-window/build/workbox-window.prod.umd.js	4.52 KB	4.52 KB	0%	1.85 KB

Workbox Aggregate Size Plugin

3.51KB gzip'ed (23% of limit)
7.93KB uncompressed

[philipwalton]

LGTM

[coveralls]

Coverage remained the same at 79.293% when pulling 28f3142 on precaching-cache-control into 1149f5f on master.