1634 Add in_app_purchase for readme and replace pub.dartlang.org to pub.dev. (cla: yes)

1637 [in_app_purchase] Expanded description (cla: yes)

1638 [image_picker] ios:  support GIF animation and the scaling (cla: yes)

1639  [cloud_functions]:Replace call with getHttpsCallable under Usage section in readme (cla: yes)

1640 [google_maps_flutter] Update and comment out the ‘set marker icon’ sample. (cla: yes)

1641 [android_alarm_manager] Move method channel usage to the platform main thread (cla: yes)

1642 [firebase_ml_vision] Update sample to use new ImageStreamListener API (cla: yes)

1643 suppress deprecation warning for BinaryMessages (cla: yes)