Add skyfunction to return all registered toolchain labels.

Part of #2219.

Change-Id: I7293fd13bd8e0931f92afd051e18a9e7ce63762d
PiperOrigin-RevId: 161721445
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/BUILD b/src/test/java/com/google/devtools/build/lib/skyframe/BUILD
index 9af05dd..d68e4e8 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/BUILD
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/BUILD
@@ -25,6 +25,7 @@
         "//src/main/java/com/google/devtools/build/lib:vfs",
         "//src/main/java/com/google/devtools/build/lib/actions",
         "//src/main/java/com/google/devtools/build/lib/cmdline",
+        "//src/main/java/com/google/devtools/build/lib/rules/platform",
         "//src/main/java/com/google/devtools/build/skyframe",
         "//src/main/java/com/google/devtools/build/skyframe:skyframe-objects",
         "//src/test/java/com/google/devtools/build/lib:actions_testutil",
@@ -69,8 +70,10 @@
         "//src/main/java/com/google/devtools/build/lib:util",
         "//src/main/java/com/google/devtools/build/lib:vfs",
         "//src/main/java/com/google/devtools/build/lib/actions",
+        "//src/main/java/com/google/devtools/build/lib/analysis/platform",
         "//src/main/java/com/google/devtools/build/lib/cmdline",
         "//src/main/java/com/google/devtools/build/lib/rules/cpp",
+        "//src/main/java/com/google/devtools/build/lib/rules/platform",
         "//src/main/java/com/google/devtools/build/skyframe",
         "//src/main/java/com/google/devtools/build/skyframe:skyframe-objects",
         "//src/test/java/com/google/devtools/build/lib:actions_testutil",
@@ -78,6 +81,7 @@
         "//src/test/java/com/google/devtools/build/lib:foundations_testutil",
         "//src/test/java/com/google/devtools/build/lib:packages_testutil",
         "//src/test/java/com/google/devtools/build/lib:testutil",
+        "//src/test/java/com/google/devtools/build/lib/rules/platform:testutil",
         "//third_party:guava",
         "//third_party:guava-testlib",
         "//third_party:jsr305",