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

runtime/vm/stub_code_mips.cc

Index: runtime/vm/stub_code_mips.cc
===================================================================
--- runtime/vm/stub_code_mips.cc	(revision 36530)
+++ runtime/vm/stub_code_mips.cc	(working copy)
@@ -26,6 +26,7 @@
     "Set to true for debugging & verifying the slow paths.");
 DECLARE_FLAG(bool, trace_optimized_ic_calls);
 
+DECLARE_FLAG(bool, enable_debugger);
 
 // Input parameters:
 //   RA : return address.
@@ -1424,22 +1425,24 @@
 #endif  // DEBUG
 
 
-  // Check single stepping.
-  Label not_stepping;
-  __ lw(T0, FieldAddress(CTX, Context::isolate_offset()));
-  __ lbu(T0, Address(T0, Isolate::single_step_offset()));
-  __ BranchEqual(T0, 0, &not_stepping);
-  // Call single step callback in debugger.
-  __ EnterStubFrame();
-  __ addiu(SP, SP, Immediate(-2 * kWordSize));
-  __ sw(S5, Address(SP, 1 * kWordSize));  // Preserve IC data.
-  __ sw(RA, Address(SP, 0 * kWordSize));  // Return address.
-  __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
-  __ lw(RA, Address(SP, 0 * kWordSize));
-  __ lw(S5, Address(SP, 1 * kWordSize));
-  __ addiu(SP, SP, Immediate(2 * kWordSize));
-  __ LeaveStubFrame();
-  __ Bind(&not_stepping);
+  if (FLAG_enable_debugger) {
+    // Check single stepping.
+    Label not_stepping;
+    __ lw(T0, FieldAddress(CTX, Context::isolate_offset()));
+    __ lbu(T0, Address(T0, Isolate::single_step_offset()));
+    __ BranchEqual(T0, 0, &not_stepping);
+    // Call single step callback in debugger.
+    __ EnterStubFrame();
+    __ addiu(SP, SP, Immediate(-2 * kWordSize));
+    __ sw(S5, Address(SP, 1 * kWordSize));  // Preserve IC data.
+    __ sw(RA, Address(SP, 0 * kWordSize));  // Return address.
+    __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
+    __ lw(RA, Address(SP, 0 * kWordSize));
+    __ lw(S5, Address(SP, 1 * kWordSize));
+    __ addiu(SP, SP, Immediate(2 * kWordSize));
+    __ LeaveStubFrame();
+    __ Bind(&not_stepping);
+  }
 
   // Load argument descriptor into S4.
   __ lw(S4, FieldAddress(S5, ICData::arguments_descriptor_offset()));