Stop a blink of the final position of shared element.

Sometimes a frame from the final layout position of the shared
element was showing on the first frame of the activity showing.
This pushes the first frame to force it until after the transition
has started.

Test: manual testing

Change-Id: I831ed4b419eaadf1aad9d5efbeb99f04eebd0640

core/java/android/app/EnterTransitionCoordinator.java

@@ -90,7 +90,7 @@ class EnterTransitionCoordinator extends ActivityTransitionCoordinator {
                                     decorView.getViewTreeObserver().removeOnPreDrawListener(this);
                                 }
                             }
-                            return mIsReadyForTransition;
+                            return false;
                         }
                     });
         }