Write protect executable pages in the VM.

runtime/vm/code_patcher.h

Index: runtime/vm/code_patcher.h
diff --git a/runtime/vm/code_patcher.h b/runtime/vm/code_patcher.h
index c0f4799dba1675cc22909939ca693e2667e97f98..3143facccf8540b0f1c5316f4c0c92e03e415142 100644
--- a/runtime/vm/code_patcher.h
+++ b/runtime/vm/code_patcher.h
@@ -22,6 +22,17 @@ class RawICData;
 class RawObject;
 class String;
 
+class WritableInstructionsScope : public ValueObject {
+ public:
+  WritableInstructionsScope(uword address, intptr_t size);
+  ~WritableInstructionsScope();
+
+ private:
+  uword address_;
+  intptr_t size_;
+};
+
+
 class CodePatcher : public AllStatic {
  public:
   // Dart static calls have a distinct, machine-dependent code pattern.