Warn when modifying shared instances of Array and Dict to prepare for implicit sharing.

Status Job ID Name Coverage
  Build
passed #1124365
build

00:03:09

passed #1124370
build_android

00:02:00

passed #1124366
build_clang_libcpp

00:03:11

passed #1124369
build_clazy

00:02:59

passed #1124368
build_mingw64_fedora

00:02:39

passed #1124367
build_ubuntu_16_04

00:01:25