3115 [plugin_platform_interface] Migrate to null safety (cla: yes)

3116 [integration_test] Add watchPerformance (cla: yes, waiting for test harness)

3117 [webview_flutter] Android Code Inspection and Clean up (cla: yes)

3119 [video_player] fix Timer Leak (cla: yes)

3120 [in_app_purchase] Android Code Inspection and Clean up (cla: yes)

3122 [video_player] Fix SSLProtocolException for low API version (cla: yes)

3123 Fixes Playing video from asset on Android (cla: yes)

3124 [camera] Camera fix android audio (cla: yes)

3125 [url_launcher] Handling the ActivityNotFoundExeption. (cla: yes)