WebContentsObserver and TabObserver update for PlzNavigate

chrome/android/java/src/org/chromium/chrome/browser/tab/EmptyTabObserver.java

Index: chrome/android/java/src/org/chromium/chrome/browser/tab/EmptyTabObserver.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/tab/EmptyTabObserver.java b/chrome/android/java/src/org/chromium/chrome/browser/tab/EmptyTabObserver.java
index 40b364c30b3946090ad021ac70123f5fe07eccea..85838e4516fde14b625af6d7ebb140838d645c8a 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/tab/EmptyTabObserver.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/tab/EmptyTabObserver.java
@@ -98,7 +98,16 @@ public class EmptyTabObserver implements TabObserver {
             boolean isNavigationToDifferentPage, boolean isFragmentNavigation, int statusCode) { }
 
     @Override
-    public void didFirstVisuallyNonEmptyPaint(Tab tab) { }
+    public void onDidStartNavigation(
+            Tab tab, String url, boolean isInMainFrame, boolean isErrorPage) {}
+
+    @Override
+    public void onDidFinishNavigation(Tab tab, String url, boolean isInMainFrame,
+            boolean isErrorPage, boolean hasCommitted, boolean isSamePage, boolean isReload,
+            int errorCode) {}
+
+    @Override
+    public void didFirstVisuallyNonEmptyPaint(Tab tab) {}
 
     @Override
     public void onDidChangeThemeColor(Tab tab, int color) { }