Added option to allow verification of objects on the stack.

Currently it's defined out by VERIFY_OBJECT_ENABLED. Also made various
fixes to allow heap object verification to work again.

(cherry picked from commit d4983495782be8d54c9c1f0266dc52395b947724)

Change-Id: Icd625e1e0dc240c0ad1d10e2c58c7d5d63fec030
diff --git a/src/runtime.cc b/src/runtime.cc
index b340317..1378229 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -642,6 +642,7 @@
                    options->heap_growth_limit_,
                    options->heap_maximum_size_,
                    options->image_);
+  heap_->EnableObjectValidation();
 
   BlockSignals();