Direct backend object allocation API

Change-Id: Ie8733a4db8061c67678a41cf239ce4407e967df7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/212965
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index a0b3e17..ce2fcdd 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1643,6 +1643,9 @@
   import("gn/tests.gni")
   test_lib("tests") {
     sources = tests_sources + pathops_tests_sources
+    if (skia_use_metal) {
+      sources += metal_tests_sources
+    }
     if (!skia_enable_fontmgr_android) {
       sources -= [ "//tests/FontMgrAndroidParserTest.cpp" ]
     }