feed: Always enroll chrome users into spinner experiment

This experiment evaluates the impact of a bug fix on power metrics. The
bug caused the feed spinner to continue running 60fps animation tasks
in the background. It turns out that, when this continues after Chrome
goes into the background, it can cause Android to terminate Chrome
earlier.

Currently, users only enroll into a Finch group when the feed spinner
is first shown. This doesn't happen in all browsing sessions. As a
result, the Finch data is skewed towards shorter browser process
lifetimes in one group.

To work around this, this patch checks the feature's flag value after
Chrome's native startup, thereby enrolling every user and browsing
session into one of the Finch groups. This way, we can draw
conclusions on the power impact of this bug for any user, and
including any impact on cold starts.

Bug: 1151391
Change-Id: I2ca59c9539f1bab7bfafe12ad61e59f0a7a8aae3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2642628
Auto-Submit: Eric Seckler <eseckler@chromium.org>
Commit-Queue: Michael Thiessen <mthiesse@chromium.org>
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846143}

chrome/android/java/src/org/chromium/chrome/browser/app/ChromeActivity.java

@@ -1428,6 +1428,14 @@ public abstract class ChromeActivity<C extends ChromeActivityComponent>
                             getTabModelSelector()),
                     AsyncTabParamsManagerSingleton.getInstance());
         }
+
+        // Make sure the user is reporting into one of the feed spinner groups, so that we can
+        // analyze daily power impact for a typical Chrome user. The flag only has an effect if the
+        // spinner is shown, but our earlier UMA analysis shows that it may have a side-effect on
+        // a future browsing session's power, even if the spinner is not shown (by causing more
+        // cold-starts).
+        // TODO(crbug.com/1151391): Remove after analysis is complete.
+        ChromeFeatureList.isEnabled(ChromeFeatureList.INTEREST_FEED_SPINNER_ALWAYS_ANIMATE);
     }
 
     /**