[libfuzzer] fetch libfuzzer on mac and register it in build root.

Partial resubmit of https://crrev.com/e9aba58f6cbfee6fec2af0ec4832a3c23ec66b9f

BUG=597066

Review URL: https://codereview.chromium.org/1885093004

Cr-Commit-Position: refs/heads/master@{#387670}
diff --git a/DEPS b/DEPS
index 353d71f..56f6187 100644
--- a/DEPS
+++ b/DEPS
@@ -278,6 +278,10 @@
 
   'src/third_party/re2/src':
     Var('chromium_git') + '/external/github.com/google/re2.git' + '@' + 'dba3349aba83b5588e85e5ecf2b56c97f2d259b7',
+
+  # Used for building libFuzzers (only supports Linux).
+  'src/third_party/libFuzzer/src':
+    Var('chromium_git') + '/chromium/llvm-project/llvm/lib/Fuzzer.git' + '@' +  Var('libfuzzer_revision'),
 }
 
 
@@ -419,10 +423,6 @@
     # Wireless Display Software. Used on Chrome OS.
     'src/third_party/wds/src':
      Var('chromium_git') + '/external/github.com/01org/wds' + '@' + 'f187dda5fccaad08e168dc6657109325f42c648e',
-
-    # Used for building libFuzzers (only supports Linux).
-    'src/third_party/libFuzzer/src':
-     Var('chromium_git') + '/chromium/llvm-project/llvm/lib/Fuzzer.git' + '@' +  Var('libfuzzer_revision'),
   },
   'android': {
     'src/third_party/android_protobuf/src':