Use the instruction iterator rather than an explicit loop in more places.

runtime/vm/il_printer.cc

Index: runtime/vm/il_printer.cc
diff --git a/runtime/vm/il_printer.cc b/runtime/vm/il_printer.cc
index 10b172406df5f385eab2dec5344a36cbd358a1c4..1d33db8258171a8f89bbdedee61b048de87bf10c 100644
--- a/runtime/vm/il_printer.cc
+++ b/runtime/vm/il_printer.cc
@@ -531,10 +531,9 @@ void FlowGraphVisualizer::PrintFunction() {
         Print("0 0 ");  // Required fields "bci" and "use". Unused.
         PrintInstruction(block_order_[i]);
         // And all the successors until an exit, branch, or a block entry.
-        Instruction* current = block_order_[i];
-        for (ForwardInstructionIterator it(current->AsBlockEntry());
-             !it.Done();
-             it.Advance()) {
+        BlockEntryInstr* entry = block_order_[i];
+        Instruction* current = entry;
+        for (ForwardInstructionIterator it(entry); !it.Done(); it.Advance()) {
           current = it.Current();
           Print("0 0 ");
           PrintInstruction(current);