[Paint Preview] Fix ficker issue on upgrade to live page

This attempts to decrease the inconsistensies between the paint preview
and the live page by delaying the removing of paint preview until both
onPageLoadFinished AND didFirstVisuallNonEmptyPaint happen.

Bug: 1111006
Change-Id: I66c46cc9454608a92b6b6f09c2beba60668b431f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2327278
Commit-Queue: Mehran Mahmoudi <mahmoudi@chromium.org>
Reviewed-by: Fred Mello <fredmello@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792884}

chrome/browser/paint_preview/android/java/src/org/chromium/chrome/browser/paint_preview/TabbedPaintPreviewPlayer.java

@@ -79,10 +79,26 @@ public class TabbedPaintPreviewPlayer implements TabViewProvider, UserData {
         mTab = tab;
         mPaintPreviewTabService = PaintPreviewTabServiceFactory.getServiceInstance();
         mTabObserver = new EmptyTabObserver() {
+            private boolean mFirstPaintHappened;
+            private boolean mPageLoadFinished;
+
             @Override
             public void didFirstVisuallyNonEmptyPaint(Tab tab) {
-                if (!isShowingAndNeedsBadge()) return;
+                mFirstPaintHappened = true;
+                maybeRemovePaintPreview();
+            }
+
+            @Override
+            public void onPageLoadFinished(Tab tab, String url) {
+                mPageLoadFinished = true;
+                maybeRemovePaintPreview();
+            }
+
+            private void maybeRemovePaintPreview() {
+                if (!isShowingAndNeedsBadge() || !mFirstPaintHappened || !mPageLoadFinished) return;
 
+                mFirstPaintHappened = false;
+                mPageLoadFinished = false;
                 long delayMs = ChromeFeatureList.getFieldTrialParamByFeatureAsInt(
                         ChromeFeatureList.PAINT_PREVIEW_SHOW_ON_STARTUP, INITIAL_REMOVE_DELAY_PARAM,
                         DEFAULT_INITIAL_REMOVE_DELAY_MS);