Make Blink test targets generally visible.

public/BUILD.gn

Index: public/BUILD.gn
diff --git a/public/BUILD.gn b/public/BUILD.gn
index b5621ba3b124cd11e786188aa0332c430ae438e3..0e56d86042a8873b4653ffe9e537f6aa85b07649 100644
--- a/public/BUILD.gn
+++ b/public/BUILD.gn
@@ -68,6 +68,24 @@ group("all_blink") {
   ]
 }
 
+group("blink_tests") {
+  testonly = true
+
+  deps = [
+    "//third_party/WebKit/Source/platform:heap_unittests",
+    "//third_party/WebKit/Source/platform:platform_unittests",
+    "//third_party/WebKit/Source/wtf:wtf_unittests",
+  ]
+
+  if (is_mac) {
+    # TODO(GYP): Re-enable this as soon as we can link Blink binaries on mac.
+    deps -= [
+      "//third_party/WebKit/Source/platform:heap_unittests",
+      "//third_party/WebKit/Source/platform:platform_unittests",
+    ]
+  }
+}
+
 config("blink_headers_config") {
   include_dirs = [ ".." ]
 }