[cast_core] Introduce //third_party/cast_core

Public CastCore components will be consumed from the new repository.

Bug: b/198329453
Test: Manual verification, but linkage deferred to future change
Change-Id: If04ca7ccc1d37ff21c0d6731da042f8a5b068147
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3161412
Reviewed-by: Alex Gough <[email protected]>
Reviewed-by: Conley Owens <[email protected]>
Reviewed-by: Charlie Reis <[email protected]>
Commit-Queue: Shawn Quereshi <[email protected]>
Cr-Commit-Position: refs/heads/main@{#923035}
diff --git a/DEPS b/DEPS
index 43b320e..d987a021 100644
--- a/DEPS
+++ b/DEPS
@@ -962,6 +962,9 @@
       'dep_type': 'cipd',
   },
 
+  'src/third_party/cast_core/public/src':
+    Var('chromium_git') + '/cast_core/public' + '@' + '3ca33709a8b745f1e2492fba3aa969d9cef70029',
+
   'src/third_party/catapult':
     Var('chromium_git') + '/catapult.git' + '@' + Var('catapult_revision'),