Add histogram for pages to open enum on session restore.

Add histogram for pages to open enum on session restore.

BUG=262977

[meacer, 2013-07-27 01:29:36]

This is to add the histograms for "Open pages on startup" setting.

Originally there are only four enums: HOMEPAGE, LAST (continue from where I left
off), NEWTAB and URLs (see session_startup_pref.h).

However, we decided to have separate histogram bins for open one URL and open
multiple URLs, so the CL is a bit more complicated than it should probably be.

I'm also thinking whether we should keep the histogram bins the same as enum
values, and add another histogram for the number of opened URLs for URLS enum.

[bbudge, 2013-07-27 10:49:06]

Nits mostly.

I like your idea of a separate histogram for startup page count.

https://codereview.chromium.org/20582004/diff/2001/chrome/browser/prefs/pref_...
File chrome/browser/prefs/pref_metrics_service.cc (right):

https://codereview.chromium.org/20582004/diff/2001/chrome/browser/prefs/pref_...
chrome/browser/prefs/pref_metrics_service.cc:23: class StartupPagePref {
Why not just declare an enum named StartupPagePref or StartupPageType?

https://codereview.chromium.org/20582004/diff/2001/chrome/browser/prefs/pref_...
chrome/browser/prefs/pref_metrics_service.cc:30: NO_URL = 4,
ZERO_URLS ?

[meacer, 2013-07-30 00:37:55]

FYI: The CL for the other patch I proposed is here (separate histograms for the
startup setting and the number of URLs to open):
https://codereview.chromium.org/21121007/

https://codereview.chromium.org/20582004/diff/2001/chrome/browser/prefs/pref_...
File chrome/browser/prefs/pref_metrics_service.cc (right):

https://codereview.chromium.org/20582004/diff/2001/chrome/browser/prefs/pref_...
chrome/browser/prefs/pref_metrics_service.cc:23: class StartupPagePref {
On 2013/07/27 10:49:06, bbudge1 wrote:
> Why not just declare an enum named StartupPagePref or StartupPageType?

Done.

https://codereview.chromium.org/20582004/diff/2001/chrome/browser/prefs/pref_...
chrome/browser/prefs/pref_metrics_service.cc:30: NO_URL = 4,
On 2013/07/27 10:49:06, bbudge1 wrote:
> ZERO_URLS ?

Done.

[bbudge, 2013-12-04 20:05:09]

lgtm with one coment.

https://codereview.chromium.org/20582004/diff/10001/chrome/browser/prefs/pref...
File chrome/browser/prefs/pref_metrics_service.cc (right):

https://codereview.chromium.org/20582004/diff/10001/chrome/browser/prefs/pref...
chrome/browser/prefs/pref_metrics_service.cc:23: enum StartupPagePref {
Also, since it's private to this file, could this be defined in an anonymous
namespace above?