Add UMA metric to track the time elapsed since a WebAPK was last launched

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappActivity.java

Index: chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappActivity.java
index 5ca863096b36d819eac0d67cdd363465992cb0c1..7d2c2d4404894bb08b2c8375a55cbba09b951769 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappActivity.java
@@ -405,10 +405,15 @@ public class WebappActivity extends FullScreenActivity {
         // app is not directly launched from the home screen, as this interferes
         // with the heuristic.
         if (mWebappInfo.isLaunchedFromHomescreen()) {
+            onWillUpdateLastUsedTime(storage);

[dominickn, 2017/06/08 05:15:27]

It would be good if you could add a quick test that after installing a webapp,
wasLaunched() is false, and then after launch, it's true.

[pkotwicz, 2017/06/12 20:34:46]

How do you suggest that I add such a test? I don't think that I can write the
test that you want as a JUnit test. I have already added two integration tests
as part of this CL

I could test that registering a webapp does not cause WebappDataStorage to think
that the webapp has been launched.

[dominickn, 2017/06/14 00:19:39]

Ah yes, the integration test is sufficient with another assert. Thanks

+            storage.setWasLaunched();

[dominickn, 2017/06/08 05:15:27]

I think you need to setWasLaunched() before onWillUpdateLastUsedTime()

[pkotwicz, 2017/06/12 20:34:46]

Actually, it is important for the WebApkActivity method to be run before
WebappDataStorage#setHasBeenLaunched() is called because WebApkActivity needs to
know whether the lauch is the first launch.

I have changed around the code. Hopefully, it is clearer now

             storage.updateLastUsedTime();
         }
     }
 
+    /** Called prior to updating the "last used" time in WebappDataStorage. */
+    protected void onWillUpdateLastUsedTime(WebappDataStorage storage) {}
+
     protected void initializeSplashScreenWidgets(int backgroundColor, Bitmap splashImage) {
         Bitmap displayIcon = splashImage == null ? mWebappInfo.icon() : splashImage;
         int minimiumSizeThreshold = getResources().getDimensionPixelSize(