Add function for generating validation signatures.

DEPS

 # DEPS files look like -*- Python -*-
 
 vars = {
   # These two should be updated to the same revision whenever possible.
   "x86_toolchain_version": "7819",
   "pnacl_toolchain_version": "7819",
 
   # ARM trusted toolchain version cannot be changed for now.
   "arm_trusted_toolchain_version": "7000",
 
@@ skipping 55 matching lines @@
   "third_party/jsoncpp/source/src/lib_json":
     (Var("sourceforge_url") % {"repo": "jsoncpp"}) +
         "/trunk/jsoncpp/src/lib_json@" + Var("jsoncpp_revision"),
   "third_party/lcov":
     Var("chromium_trunk") + "/src/third_party/lcov@" + Var("lcov_rev"),
   "third_party/lss":
     ((Var("googlecode_url") % "linux-syscall-support") +
      "/trunk/lss@" + Var("lss_rev")),
   "third_party/khronos":
     Var("chromium_trunk") + "/src/third_party/khronos@" + Var("chrome_rev"),
+  "third_party/openssl":
+    Var("chromium_trunk") + "/deps/third_party/openssl@" + Var("chrome_rev"),
   "third_party/ply":
     Var("chromium_trunk") + "/src/third_party/ply@" + Var("chrome_rev"),
   "third_party/pyftpdlib":
     Var("chromium_trunk") + "/src/third_party/pyftpdlib@" + Var("chrome_rev"),
   "third_party/pyftpdlib/src":
     (Var("googlecode_url") % "pyftpdlib") + "/trunk@888",
   "third_party/simplejson":
     (Var("chromium_trunk") + "/tools/build/third_party/simplejson@" +
      Var("chrome_rev")),
   "third_party/tlslite":
@@ skipping 27 matching lines @@
                "--x86-version", Var("x86_toolchain_version"),
                "--arm-trusted-version", Var("arm_trusted_toolchain_version"),
                "--pnacl-version", Var("pnacl_toolchain_version"),
                "--keep"],
   },
   {
     "pattern": ".",
     "action": ["python", "native_client/build/gyp_nacl"],
   },
 ]