VM: Propagate non-nullness from instance calls.

runtime/vm/flow_graph_inliner.cc

Index: runtime/vm/flow_graph_inliner.cc
diff --git a/runtime/vm/flow_graph_inliner.cc b/runtime/vm/flow_graph_inliner.cc
index 06f46b987613e3c88c4b307ac997a6479891f5bb..88f3575ff58b73d8ba031aebe22e6822831655a1 100644
--- a/runtime/vm/flow_graph_inliner.cc
+++ b/runtime/vm/flow_graph_inliner.cc
@@ -158,8 +158,12 @@ class GraphInfoCollector : public ValueObject {
          block_it.Advance()) {
       for (ForwardInstructionIterator it(block_it.Current()); !it.Done();
            it.Advance()) {
-        ++instruction_count_;
         Instruction* current = it.Current();
+        // Don't count instructions that won't generate any code.
+        if (current->IsRedefinition()) {
+          continue;
+        }
+        ++instruction_count_;
         if (current->IsInstanceCall() || current->IsStaticCall() ||
             current->IsClosureCall()) {
           ++call_site_count_;