customtabs: Send time to first contentful paint to the caller.

chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java

Index: chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java
index a8df5211de0d040a2abf091b6cd20d2de820fde3..cea82fde8e9994c7cd2957611a9f061d29bd18f3 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java
@@ -69,6 +69,8 @@ import java.util.concurrent.atomic.AtomicReference;
 public class CustomTabsConnection {
     private static final String TAG = "ChromeConnection";
     private static final String LOG_SERVICE_REQUESTS = "custom-tabs-log-service-requests";
+    public static final int PAGE_LOAD_METRIC = 42;
+
     @VisibleForTesting
     static final String NO_PRERENDERING_KEY =
             "android.support.customtabs.maylaunchurl.NO_PRERENDERING";
@@ -552,6 +554,30 @@ public class CustomTabsConnection {
     }
 
     /**
+     * Notifies the application of a page load metric.
+     *
+     * TODD(lizeb): Move this to a proper method in {@link CustomTabsCallback} once one is
+     * available.
+     *
+     * @param session Session identifier.
+     * @param metricName Name of the page load metric.
+     * @param offsetMs Offset in ms from navigationStart.
+     */
+    boolean notifyPageLoadMetric(CustomTabsSessionToken session, String metricName, long offsetMs) {
+        CustomTabsCallback callback = mClientManager.getCallbackForSession(session);
+        if (callback == null) return false;
+        Bundle args = new Bundle();
+        args.putLong(metricName, offsetMs);
+        try {
+            callback.onNavigationEvent(PAGE_LOAD_METRIC, args);
+        } catch (Exception e) {
+            // Pokemon exception handling, see above and crbug.com/517023.
+            return false;
+        }
+        return true;
+    }
+
+    /**
      * Keeps the application linked with a given session alive.
      *
      * The application is kept alive (that is, raised to at least the current