Add metric to record users opening a new NTP.

chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java
index deb2e7d7807ebc83e011f1acd829cac174e46c65..d6c08f6b24a7793441f6e904024c05e3a27e1044 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java
@@ -16,6 +16,8 @@ import org.chromium.chrome.browser.ntp.snippets.SnippetsBridge;
 import org.chromium.chrome.browser.rappor.RapporServiceBridge;
 import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
+import org.chromium.chrome.browser.tabmodel.EmptyTabModelSelectorObserver;
+import org.chromium.chrome.browser.tabmodel.TabModelSelector;
 import org.chromium.chrome.browser.util.UrlUtilities;
 import org.chromium.content_public.browser.LoadUrlParams;
 import org.chromium.ui.base.PageTransition;
@@ -266,6 +268,15 @@ public final class NewTabPageUma {
     }
 
     /**
+     * Records how often new tabs with a NewTabPage are created. This helps to determine how often
+     * users navigate back to already opened NTPs.
+     * @param tabModelSelector Model selector controlling the creation of new tabs.
+     */
+    public static void monitorNTPCreation(TabModelSelector tabModelSelector) {
+        tabModelSelector.addObserver(new TabCreationRecorder());
+    }
+
+    /**
      * Records the type of load for the NTP, such as cold or warm start.
      */
     public static void recordLoadType(ChromeActivity activity) {
@@ -308,6 +319,18 @@ public final class NewTabPageUma {
     }
 
     /**
+     * Records the number of new NTPs opened in a new tab. Use through
+     * {@link NewTabPageUma#monitorNTPCreation(TabModelSelector)}.
+     */
+    private static class TabCreationRecorder extends EmptyTabModelSelectorObserver {
+        @Override
+        public void onNewTabCreated(Tab tab) {

[Michael van Ouwerkerk, 2017/03/14 16:07:36]

This seems like a really roundabout way of recording NTP instantiations. Why not
just track this from the NewTabPage constructor? We already log things like
NewTabPage.LoadType there so you could even look at that if all you need is to
count instantiations.

[fhorschig, 2017/03/14 17:30:45]

I am aware about NewTabPage.LoadType. Sadly, any existing NTP that gets kicked 
out of the memory will trigger the constructor again which is what I explicitly
want to avoid.
I need to count instances but I don't accidentally want to count navigations
back to an open NTP which triggers an instantiation.

(If NewTabPage.LoadType has that same requirement, we should consider moving it)

+            if (!NewTabPage.isNTPUrl(tab.getUrl())) return;
+            RecordUserAction.record("MobileNTPOpenedInNewTab");
+        }
+    }
+
+    /**
      * Records stats related to content suggestion visits, such as the time spent on the website, or
      * if the user comes back to the NTP. Use through
      * {@link NewTabPageUma#monitorContentSuggestionVisit(Tab, int)}.