2637 [google_maps_flutter] Introduce Platform Interface package. (cla: yes)

2639 [webview_flutter] Add onReceivedError callback  (cla: yes)

2641 Add LHLL to co-owner (cla: yes)

2643 [image_picker] Added maxDuration property to pickVideo method (cla: yes)

2646 [in_app_purchase] Fix cannot fix transaction issue (cla: yes)

2647 Upgrade dependency google_sign_in_web: ^0.9.1 (cla: yes)

2649 [google_sign_in_web] Ensure not-signed-in users are returned as null. (cla: yes, waiting for test harness)

2651 Remove Gradle hacks and upgrade SDK (cla: yes)