Add duplicate libcxx source repo paths.

Context: go/unnesting-buildtools-lib
We are moving these source files buildtools/third_party/lib*/trunk -> third_party/libcxx/lib*/trunk.

rollout plan is:
1. This Cl
2. in chromium/src merge https://chromium-review.googlesource.com/c/chromium/src/+/4666325
3. remove old buildtools/third_party/lib*/trunk paths in DEPS

work tracked here: http://shortn/_BqvAmLrzlr

Bug: chromium:1458042
Change-Id: I9ddda1617a35425bf97a7d8e3b94ac0f42a62d2f
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/4702983
Commit-Queue: Joanna Wang <jojwang@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
diff --git a/DEPS b/DEPS
index 52c0241..3678c59 100644
--- a/DEPS
+++ b/DEPS
@@ -82,6 +82,8 @@
     'dep_type': 'cipd',
   },
 
+  # TODO(chromium:1458042): Remove these paths, when chromium builds files
+  # have moved to third_party/libcxx/lib*/trunk paths.
   'src/buildtools/third_party/libc++/trunk':
     Var('chromium_git') + '/external/github.com/llvm/llvm-project/libcxx.git' + '@' + '84fb809dd6dae36d556dc0bb702c6cc2ce9d4b80',
   'src/buildtools/third_party/libc++abi/trunk':
@@ -111,6 +113,12 @@
     Var('chromium_git') + '/external/github.com/google/googletest.git' + '@' + 'af29db7ec28d6df1c7f0f745186884091e602e07',
   'src/third_party/harfbuzz-ng/src':
     Var('chromium_git') + '/external/github.com/harfbuzz/harfbuzz.git' + '@' + 'db700b5670d9475cc8ed4880cc9447b232c5e432',
+  'src/third_party/libcxx/libc++/trunk':
+    Var('chromium_git') + '/external/github.com/llvm/llvm-project/libcxx.git' + '@' + '84fb809dd6dae36d556dc0bb702c6cc2ce9d4b80',
+  'src/third_party/libcxx/libc++abi/trunk':
+    Var('chromium_git') + '/external/github.com/llvm/llvm-project/libcxxabi.git' + '@' + '8d21803b9076b16d46c32e2f10da191ee758520c',
+  'src/third_party/libcxx/libunwind/trunk':
+    Var('chromium_git') + '/external/github.com/llvm/llvm-project/libunwind.git' + '@' + 'f1c687e0aaf0d70b9a53a150e9be5cb63af9215f',
   'src/third_party/libjpeg_turbo':
     Var('chromium_git') + '/chromium/deps/libjpeg_turbo.git' + '@' + '30bdb85e302ecfc52593636b2f44af438e05e784',
   'src/third_party/nasm':