gn format: Have format sort sources

tools/gn/format_test_data/062.gn

+# Sorting, making sure we don't detach comments.
+
+sources = []
+
+sources = ["x.cc"]
+
+sources = [
+  "/a",
+  "/b",
+  "/c",
+  # End of block.
+]
+
+sources += [
+  # Start of block, separate.
+
+  "c",
+  "a",
+  "b",
+]
+
+sources += [
+  "z",
+  "z2",
+  # Attached comment.
+  "y.h",
+  "y.cc",
+  "y.mm",
+  "y.rc",
+  "a"
+]
+
+sources += [
+  "z",
+  "z2",
+
+  # Block comment.
+
+  "y.h",
+  "y.cc",
+  "y.mm",
+  "y.rc",
+  "a"
+]
+
+sources += [
+  "z",
+  "z2",
+
+  #
+  # Multiline block comment.
+  #
+
+  "y.h",
+  "y.cc",
+  "y.mm",
+  "y.rc",
+  "a"
+]
+
+# With identifiers.
+sources += [
+  "a",
+  "b",
+  "c",
+  some_other_thing,
+  abcd,
+]
+
+# With accessors.
+sources += [
+  "a",
+  wee[0],
+  "b",
+  invoker.stuff,
+  "c",
+]
+
+# Various separated blocks.
+sources -= [
+  # Fix this test to build on Windows.
+  "focus_cycler_unittest.cc",
+
+  # All tests for multiple displays: not supported on Windows Ash.
+  "wm/drag_window_resizer_unittest.cc",
+
+  # Accelerometer is only available on Chrome OS.
+  "wm/maximize_mode/maximize_mode_controller_unittest.cc",
+
+  # Can't resize on Windows Ash. http://crbug.com/165962
+  "autoclick/autoclick_unittest.cc",
+  "magnifier/magnification_controller_unittest.cc",
+  # Attached 1.
+  # Attached 2.
+  "wm/workspace/workspace_window_resizer_unittest.cc",
+  "sticky_keys/sticky_keys_overlay_unittest.cc",
+  "system/tray/media_security/multi_profile_media_tray_item_unittest.cc",
+  "virtual_keyboard_controller_unittest.cc",
+
+  # Separated at end.
+  "zzzzzzzzzzzzzz.cc",
+]
+
+sources += [
+  "srtp/crypto/include/xfm.h",
+
+  # sources
+  "srtp/srtp/ekt.c",
+  "srtp/srtp/srtp.c",
+  "srtp/crypto/rng/prng.c",
+  "srtp/crypto/rng/rand_source.c",
+]