Make Blink test targets generally visible.

This makes heap_unittests, platform_unittests and wtf_unittests targets
public, so we can refer to them outside of Blink, in Chromium's root
BUILD.gn file.

Tested with the following command line:

$ gn gen ../../out_gn/Debug
$ ninja -C ../../out_gn/Debug all_blink

With the following diff in Chromium's BUILD.gn to test the new behavior.
+group("gn_all") {
+  # This should not be linked into production and depends on test targets.
+  testonly = true
+
+  deps = [
+    "//third_party/WebKit/public:blink_tests",
+  ]
+}

BUG=None
TEST=see above
R=dpranke@chromium.org
TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/910973002

git-svn-id: svn://svn.chromium.org/blink/trunk@189894 bbb929c8-8fbe-4397-9dbb-9b2b20218538
diff --git a/third_party/WebKit/public/BUILD.gn b/third_party/WebKit/public/BUILD.gn
index 50a9e85..c49dd32 100644
--- a/third_party/WebKit/public/BUILD.gn
+++ b/third_party/WebKit/public/BUILD.gn
@@ -59,6 +59,24 @@
   }
 }
 
+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 = [ ".." ]
 }