Restore code inadvertently removed.

Code was removed by accident in:
https://android-review.googlesource.com/c/platform/art/+/1652387

Test: app startup
Bug: 183954825
Change-Id: I06d697a0b29a90d2d13dd0a19fb7f381933a6e29
diff --git a/runtime/vdex_file.cc b/runtime/vdex_file.cc
index 4e54c0d..62508f6 100644
--- a/runtime/vdex_file.cc
+++ b/runtime/vdex_file.cc
@@ -150,6 +150,20 @@
     return nullptr;
   }
 
+  if (!writable) {
+    Runtime* runtime = Runtime::Current();
+    // The runtime might not be available at this point if we're running
+    // dex2oat or oatdump.
+    if (runtime != nullptr) {
+      size_t madvise_size_limit = runtime->GetMadviseWillNeedSizeVdex();
+      Runtime::MadviseFileForRange(madvise_size_limit,
+                                   vdex->Size(),
+                                   vdex->Begin(),
+                                   vdex->End(),
+                                   vdex_filename);
+    }
+  }
+
   return vdex;
 }