HDR/macOS: Use default HDR metadata

Specify a 0.005-1,000 nit luminance by default. This is a temporary
measure in two ways:
- We should plumb this through video and the compositor, and thereby
  get the correct values.
- The default tonemapping affects the SDR range, which is undesirable.
  We should roll our own tonemapping that doesn't have this property.

This will make HDR look less washed out on barely-HDR-capable monitors,
such as the built-in Macbook Pro screens.

Bug: 1101041
Change-Id: I4db344d35f5259dbeb4191e4901e9798882a06d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2300979Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788803}

components/metal_util/hdr_copier_layer.mm

@@ -72,6 +72,9 @@ API_AVAILABLE(macos(10.15))
   if (self = [super init]) {
     base::scoped_nsprotocol<id<MTLDevice>> device(metal::CreateDefaultDevice());
     [self setWantsExtendedDynamicRangeContent:YES];
+    [self setEDRMetadata:[CAEDRMetadata HDR10MetadataWithMinLuminance:0.005
+                                                         maxLuminance:1000
+                                                   opticalOutputScale:100]];
     [self setDevice:device];
     [self setOpaque:NO];
     [self setPresentsWithTransaction:YES];