Bug 1055604 - Add animation to reveal tabs on startup (r=mcomella)

mobile/android/base/tabs/TabStrip.java

@@ -103,6 +103,9 @@ public class TabStrip extends ThemedLinearLayout {
         public void onTabChanged(Tab tab, Tabs.TabEvents msg, Object data) {
             switch (msg) {
                 case RESTORED:
+                    tabStripView.restoreTabs();
+                    break;
+
                 case ADDED:
                     tabStripView.addTab(tab);
                     break;

mobile/android/base/tabs/TabStripView.java

@@ -205,6 +205,38 @@ public class TabStripView extends TwoWayView {
         });
     }
 
+    private void animateRestoredTabs() {
+        getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() {
+            @Override
+            public boolean onPreDraw() {
+                getViewTreeObserver().removeOnPreDrawListener(this);
+
+                final List<Animator> childAnimators = new ArrayList<Animator>();
+
+                final int tabHeight = getHeight() - getPaddingTop() - getPaddingBottom();
+                final int childCount = getChildCount();
+                for (int i = 0; i < childCount; i++) {
+                    final View child = getChildAt(i);
+
+                    childAnimators.add(
+                        ObjectAnimator.ofFloat(child, "translationY", tabHeight, 0));
+                }
+
+                final AnimatorSet animatorSet = new AnimatorSet();
+                animatorSet.playTogether(childAnimators);
+                animatorSet.setDuration(ANIM_TIME_MS);
+                animatorSet.setInterpolator(ANIM_INTERPOLATOR);
+                animatorSet.addListener(animatorListener);
+
+                TransitionsTracker.track(animatorSet);
+
+                animatorSet.start();
+
+                return true;
+            }
+        });
+    }
+
     private void ensurePositionIsVisible(final int position) {
         getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() {
             @Override
@@ -244,6 +276,11 @@ public class TabStripView extends TwoWayView {
         adapter.clear();
     }
 
+    void restoreTabs() {
+        refreshTabs();
+        animateRestoredTabs();
+    }
+
     void addTab(Tab tab) {
         // Refresh the list to make sure the new tab is
         // added in the right position.