[dirmd] Use metadata mixins

Use the new "mixins" feature in dirmd.
Derive mixins from file:// links in OWNERS files.

This CL is machine-generated, in two parts.

Part 1: use mixins.

1. Save current metadata to JSON files, in ORIGINAL and REDUCED forms.
   dirmd read -form original > ~/tmp/dirmd/original.json
   dirmd read -form reduced  > ~/tmp/dirmd/reduced.json
2. Run mixins.py.
   Source code: https://gist.github.com/nodirg/b59d3df338a72a8944f957c5b3a15e22

The script finds related directories, connected by file:// links
in OWNERS files. For those directories that have the same base
name, e.g.
  components/autofill
  chrome/android/java/src/org/chromium/chrome/browser/autofill
if importing the "parent" to the "child" reduces metadata, or adds
missing metadata, extract the common metadata to COMMON_METADATA
and import it in both directories.

Part2: deduplicate metadata.
Apply same instructions as in
https://chromium-review.googlesource.com/c/chromium/src/+/2795985/16

Bug: 1179786
Change-Id: I2e6378004ce433e02f1c9360b09eb72354083bf6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2897943
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Fred Mello <fredmello@chromium.org>
Owners-Override: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Nodir Turakulov <nodir@chromium.org>
Cr-Commit-Position: refs/heads/main@{#925648}

diff --git a/services/media_session/COMMON_METADATA b/services/media_session/COMMON_METADATA
new file mode 100644
index 0000000..28cafbcc
--- /dev/null
+++ b/services/media_session/COMMON_METADATA

@@ -0,0 +1,4 @@
+monorail {
+  component: "Internals>Media>Session"
+}
+team_email: "media-dev@chromium.org"
\ No newline at end of file