Trigger the Snippets Scheduler when Resuming Activities

components/ntp_snippets/remote/remote_suggestions_scheduler.h

Index: components/ntp_snippets/remote/remote_suggestions_scheduler.h
diff --git a/components/ntp_snippets/remote/remote_suggestions_scheduler.h b/components/ntp_snippets/remote/remote_suggestions_scheduler.h
index 953592ae461dce70fdfd2e9a78a89e0511ece865..06a2be7f13111eb554b4364299c702b21fbe4f3e 100644
--- a/components/ntp_snippets/remote/remote_suggestions_scheduler.h
+++ b/components/ntp_snippets/remote/remote_suggestions_scheduler.h
@@ -13,7 +13,11 @@ namespace ntp_snippets {
 class RemoteSuggestionsScheduler {
  public:
   // External triggers to consider fetching content suggestions.
-  virtual void OnBrowserStartup() = 0;
+  // Called whenever we open or return to an Activity.

[tschumann, 2017/01/03 15:24:00]

can we be more specific?  e.g.
// Called whenever the Chrome activity is resumed (i.e. when the user switches
to chrome).

also, if this includes cold starts of chrome, please add this. From "resumed"
that's not entirely clear to me.

I guess, there's no way for us to know in which situation (warm-vs-cold start)
we are, hm?

[Michael van Ouwerkerk, 2017/01/03 16:51:08]

You can ask the activity whether it had a warm start, see
AsyncInitializationActivity#hadWarmStart(). That boolean does not change, and
resume is called repeatedly, not only for starts. So to know whether you're in
some kind of start, you can check whether
AsyncInitializationActivity#getLastUserInteractionTime() returns 0. My thinking
there is that if the user has not interacted with the activity yet, is is a
start.

[fhorschig, 2017/01/04 10:17:04]

Only a little more specific. This comment has to apply for iOS, too.
Cold starts were not included as the listener would only be triggered on warm
starts.
The old distinction was: Resume called? --> warm. Otherwise use constructor.
As we don't like time delays, the event triggered on resume will be triggered
on cold starts as well, so there is a bool telling us whether it's warm or not.
The fact that it is stored caused me to never get another value than "false".
Resume might be called everytime, but for some reason, the listener will not
get called on resume on cold starts. Not sure why and if this is WAI.
Thank you, this is perfect! I was so desperately looking for that. It found its
way into the code (in another function and commented).

[tschumann, 2017/01/04 10:51:53]

I'm leaning towards not doing anything on cold starts, so should we just special
case this signal (including the method name) to warm-starts only? [my
preference].

[jkrcal, 2017/01/04 12:21:12]

Tim, do you mean 
 - having just the warm-start signal (and throwing away part of the code of
Friedrich) or 
 - having two separate signals [my preference]?

[tschumann, 2017/01/04 12:26:30]

i'm leaning towards just the warm-start as I can't think of a reasonable way we
want to do anything on a cold-start (scheduling something based on wall-time has
a smell and unclear effects).
But i'm fine with adding both signals.

[fhorschig, 2017/01/04 12:56:10]

I added both signals as this makes it easier to drop one in case we decide
that we never use it.
This way, the heat of the start is pretty explicit, too.

+  // To keep start ups fast, defer heavy work.
+  virtual void OnBrowserResumed() = 0;
+  // Called whenever a new NTP is opened. This may be called on cold starts.
+  // So to keep start ups fast, defer heavy work for cold starts.
   virtual void OnNTPOpened() = 0;
 
   // Fetch content suggestions.