Add flag —enable-debugger (default true) in order to disable debugger single stepping code.

runtime/vm/intermediate_language_mips.cc

Index: runtime/vm/intermediate_language_mips.cc
===================================================================
--- runtime/vm/intermediate_language_mips.cc	(revision 36530)
+++ runtime/vm/intermediate_language_mips.cc	(working copy)
@@ -21,6 +21,7 @@
 
 namespace dart {
 
+DECLARE_FLAG(bool, emit_edge_counters);
 DECLARE_FLAG(int, optimization_counter_threshold);
 DECLARE_FLAG(bool, propagate_ic_data);
 DECLARE_FLAG(bool, use_osr);
@@ -4481,7 +4482,9 @@
 void TargetEntryInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   __ Bind(compiler->GetJumpLabel(this));
   if (!compiler->is_optimizing()) {
-    compiler->EmitEdgeCounter();
+    if (FLAG_emit_edge_counters) {
+      compiler->EmitEdgeCounter();
+    }
     // On MIPS the deoptimization descriptor points after the edge counter
     // code so that we can reuse the same pattern matching code as at call
     // sites, which matches backwards from the end of the pattern.
@@ -4503,7 +4506,9 @@
 void GotoInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   __ TraceSimMsg("GotoInstr");
   if (!compiler->is_optimizing()) {
-    compiler->EmitEdgeCounter();
+    if (FLAG_emit_edge_counters) {
+      compiler->EmitEdgeCounter();
+    }
     // Add a deoptimization descriptor for deoptimizing instructions that
     // may be inserted before this instruction.  On MIPS this descriptor
     // points after the edge counter code so that we can reuse the same