Exercise Heap::PreZygoteFork() in a test.

Change-Id: If41c931ffdbb0310536799b4515557770f2cd4b9
diff --git a/runtime/gc/heap_test.cc b/runtime/gc/heap_test.cc
index 73196b2..14d78d8 100644
--- a/runtime/gc/heap_test.cc
+++ b/runtime/gc/heap_test.cc
@@ -71,5 +71,17 @@
   bitmap->Set(fake_end_of_heap_object);
 }
 
+class ZygoteHeapTest : public CommonRuntimeTest {
+  void SetUpRuntimeOptions(RuntimeOptions* options) {
+    CommonRuntimeTest::SetUpRuntimeOptions(options);
+    options->push_back(std::make_pair("-Xzygote", nullptr));
+  }
+};
+
+TEST_F(ZygoteHeapTest, PreZygoteFork) {
+  // Exercise Heap::PreZygoteFork() to check it does not crash.
+  Runtime::Current()->GetHeap()->PreZygoteFork();
+}
+
 }  // namespace gc
 }  // namespace art