Propagate this-specialization to regular (megamorphic) calls

runtime/vm/flow_graph.cc

Index: runtime/vm/flow_graph.cc
diff --git a/runtime/vm/flow_graph.cc b/runtime/vm/flow_graph.cc
index 16ed1ebacf2ba492cc0366c771511fe4e3790cf0..642ec9be5d2cd31c8679abc9264b218a82c2bdbb 100644
--- a/runtime/vm/flow_graph.cc
+++ b/runtime/vm/flow_graph.cc
@@ -1996,11 +1996,17 @@ bool FlowGraph::Canonicalize() {
       Instruction* replacement = current->Canonicalize(this);
 
       if (replacement != current) {
-        // For non-definitions Canonicalize should return either NULL or
-        // this.
-        ASSERT((replacement == NULL) || current->IsDefinition());
-        ReplaceCurrentInstruction(&it, current, replacement);
         changed = true;
+
+        if (current->IsInstanceCall()) {
+          current->AsDefinition()->ReplaceWith(replacement->AsDefinition(),
+                                               &it);
+        } else {
+          // For non-definitions Canonicalize should return either NULL or
+          // this.
+          ASSERT((replacement == NULL) || current->IsDefinition());
+          ReplaceCurrentInstruction(&it, current, replacement);
+        }
       }
     }
   }