Version (gn): 403392

What steps will reproduce the problem?
gn format --stdin <<EOF
action("test") {
  sources = [ "somewhat/long/path/to/src/org/chromium/components/test/JavaClass.java" ]

  custom_variable = [ "somewhat/long/path/to/src/org/chromium/components/test/JavaClass.java" ]
}
EOF


What is the expected output?
action("test") {
  sources = [
    "somewhat/long/path/to/src/org/chromium/components/test/JavaClass.java",
  ]

  custom_variable = [
    "somewhat/long/path/to/src/org/chromium/components/test/JavaClass.java",
  ]
}


What do you see instead?
action("test") {
  sources = [
    "somewhat/long/path/to/src/org/chromium/components/test/JavaClass.java",
  ]

  custom_variable =
      [ "somewhat/long/path/to/src/org/chromium/components/test/JavaClass.java" ]
}


Discussed in https://codereview.chromium.org/2110543004/. gn format (and thus git cl format) seems to assume any "custom" variable is of a non-list type. This means list declarations like "java_files" is formatted differently than "sources", even when they both are lists.