Use a uniform way to emit code for all instructions.

runtime/vm/flow_graph_compiler_arm.cc

Index: runtime/vm/flow_graph_compiler_arm.cc
diff --git a/runtime/vm/flow_graph_compiler_arm.cc b/runtime/vm/flow_graph_compiler_arm.cc
index d1e17a8dc8418e58d3051c3daff6edf203fc2554..a0b8be2ab79b9f0f0b069d5700c5853a7d791ad2 100644
--- a/runtime/vm/flow_graph_compiler_arm.cc
+++ b/runtime/vm/flow_graph_compiler_arm.cc
@@ -638,12 +638,7 @@ void FlowGraphCompiler::EmitInstructionPrologue(Instruction* instr) {
       AddCurrentDescriptor(PcDescriptors::kDeopt,
                            assert->deopt_id(),
                            assert->token_pos());
-    } else if (instr->IsGuardField()) {
-      GuardFieldInstr* guard = instr->AsGuardField();
-      AddCurrentDescriptor(PcDescriptors::kDeopt,
-                           guard->deopt_id(),
-                           Scanner::kDummyTokenIndex);
-    } else if (instr->CanBeDeoptimizationTarget()) {
+    } else if (instr->CanBeDeoptimizationTarget() || instr->IsGuardField()) {
       AddCurrentDescriptor(PcDescriptors::kDeopt,
                            instr->deopt_id(),
                            Scanner::kDummyTokenIndex);