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NSNumber literals, expression literals, container literals: e.g. in
base/mac/foundation_util.mm (expression literal),
base/mac/foundation_util_unittests.mm (NSNumber literal, container literal).
This is a compiler feature and we have used it for years.
https://clang.llvm.org/docs/ObjectiveCLiterals.html

@implementation instance variables, in translate_bubble_controller.h
(note that ivars referred to in the _unittest.mm need to stay in the .h).
This requires the "modern runtime". We could use this once we we shipped
64-bit chrome (m39, late 2014).

NSDictionary and NSArray subscripting, e.g. in service_process_util_mac.mm.
Note that for scoped_nsobject<NSArray>, you need to do ptr.get()[index].
(We could probably return a proxy object from scoped_nsobject::operator[]
to make that unnecessary, but that feels like it might be too clever.)
Custom @interfaces can add their own support for subscripting.
This has worked since the 10.8 SDK.

Generics, e.g. in translate_bubble_controller.h: NSDictionary<NSNumber*, NSView*>
instead of just NSDictionary.  This works only since the 10.11 SDK, and the
bots had an older SDK until erikchen's 10.12 SDK work completed late last year.

https://developer.apple.com/videos/play/wwdc2012/405/, click "slides", auth
See also https://developer.apple.com/library/content/releasenotes/ObjectiveC/ObjCAvailabilityIndex/index.html

We don't use property auto-synthesis because it's very magical. We build
with -Wobjc-missing-property-synthesis to make sure the compiler informs
us if we forget to synthesize a property in some way.

We don't use arc.

Bug: 324079
Change-Id: I78659ed47829fe73c2b87cce43a83ec36deb87e8
Reviewed-on: https://chromium-review.googlesource.com/884011
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531990}