Enable page caching and CSS/JS aggregation by default in the Standard install profile

#606840: Enable internal page cache by default and other issues already did this for Drupal 8. Let's consider doing it for Drupal 7 too.

We would do it in the Standard install profile only, since "Minimal" is intended to be minimal (and for advanced users).

I think the main question to discuss here is whether it's a useful feature for the average Drupal 7 site:

• Is the anonymous traffic expected to be high enough for page caching to be worth it?
• Is the rate at which the site is changing expected to be low enough for page caching to be worth it?

Certainly if you look around the Internet and poke into the HTML responses of Drupal sites, you do see a lot of sites that forgot to turn on CSS/JS aggregation (and probably page caching too, although that's not something I've looked at closely). Doing it in the install profile would hopefully make it easier for site builders to do the right thing.

It would be interesting to get feedback from Drupal 7 site builders regarding the above questions.

(And also on this secondary question: Do you use the Standard install profile in a way that it would be annoying to have these features turned on during development of the site? But in answering that part, try to think about whether you are the intended audience of the Standard profile, or whether you are using it despite being more "advanced" than the typical user of that profile.)

With this patch, we would enable it for real sites that use the Standard install profile, but exclude it when the Standard install profile is used during automated tests. This is because a lot of core and contrib tests that use this profile are written under the assumption that page caching is off, and we don't want to pull the rug out from under them. Note that there are also some "stale-content" type bugs that occur in core when page caching is turned on (see test results in #606840-118: Enable internal page cache by default and bug reports linked later on in that issue). Those bugs of course exist either way (and are currently experienced on any Drupal 7 production site that has page caching turned on) and should ideally be fixed regardless of whether page caching is turned on by default in the Standard install profile.

There is further discussion of the pros and cons of this in the above-linked issue.