Update V8 DEPS.

Rolling v8/tools/clang to 6f504ec1a843c7c6af799768a774dec205ce4f3b

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/822073003

Cr-Commit-Position: refs/heads/master@{#25942}

DEPS

@@ -18,7 +18,7 @@ deps = {
   "v8/testing/gmock":
     Var("git_url") + "/external/googlemock.git" + "@" + "29763965ab52f24565299976b936d1265cb6a271",  # from svn revision 501
   "v8/tools/clang":
-    Var("git_url") + "/chromium/src/tools/clang.git" + "@" + "90fb65e7a9a5c9d6d9613dfb0e78921c52ca9cfc",
+    Var("git_url") + "/chromium/src/tools/clang.git" + "@" + "6f504ec1a843c7c6af799768a774dec205ce4f3b",
 }
 
 deps_os = {