Use a uniform way to emit code for all instructions.

runtime/vm/flow_graph_compiler_mips.cc

Index: runtime/vm/flow_graph_compiler_mips.cc
diff --git a/runtime/vm/flow_graph_compiler_mips.cc b/runtime/vm/flow_graph_compiler_mips.cc
index 4b88a5fd87304b0ea38f13b6fd7480c22238d043..e3c92d1fdc42d3c40f2d56e2ec0f35e20eb276b6 100644
--- a/runtime/vm/flow_graph_compiler_mips.cc
+++ b/runtime/vm/flow_graph_compiler_mips.cc
@@ -570,12 +570,7 @@ 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);