[benchmark] Share BoringSSL between FfiBoringssl implementations.

The Dart benchmarks will soon be forked for non-nullability and there
will be two implementations of the FfiBoringssl benchmark. This change
moves the native BoringSSL build a level up so it can be shared between
the two implementations, avoiding doubling the needed filesystem space.

Change-Id: I8bcc113e19715865f28bc1950cf07ba6cc7ea61f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/148760
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Jonas Termansen <sortie@google.com>

DEPS

@@ -477,7 +477,7 @@ deps = {
 
   # TODO(37531): Remove these cipd packages and build with sdk instead when
   # benchmark runner gets support for that.
-  Var("dart_root") + "/benchmarks/FfiBoringssl/dart/native/out/": {
+  Var("dart_root") + "/benchmarks/FfiBoringssl/native/out/": {
       "packages": [
           {
               "package": "dart/benchmarks/ffiboringssl",

benchmarks/FfiBoringssl/dart/digest.dart

@@ -14,9 +14,9 @@ import 'types.dart';
 DynamicLibrary openSsl() {
   // Force load crypto.
   dlopenPlatformSpecific("crypto",
-      path: Platform.script.resolve("native/out/").path);
+      path: Platform.script.resolve("../native/out/").path);
   DynamicLibrary ssl = dlopenPlatformSpecific("ssl",
-      path: Platform.script.resolve("native/out/").path);
+      path: Platform.script.resolve("../native/out/").path);
   return ssl;
 }