Write protect executable pages in the VM.

runtime/vm/assembler.cc

Index: runtime/vm/assembler.cc
diff --git a/runtime/vm/assembler.cc b/runtime/vm/assembler.cc
index 5a8f846dc6832bfe7bda8bb80750001bec67b58b..ff08c9a2d76cd6bd9774c4da20fd10358529c488 100644
--- a/runtime/vm/assembler.cc
+++ b/runtime/vm/assembler.cc
@@ -149,12 +149,25 @@ class PatchCodeWithHandle : public AssemblerFixup {
     pointer_offsets_->Add(position);
   }
 
+  virtual bool IsPointerOffset() const { return true; }
+
  private:
   ZoneGrowableArray<intptr_t>* pointer_offsets_;
   const Object& object_;
 };
 
 
+intptr_t AssemblerBuffer::CountPointerOffsets() const {
+  intptr_t count = 0;
+  AssemblerFixup* current = fixup_;
+  while (current != NULL) {
+    if (current->IsPointerOffset()) ++count;
+    current = current->previous_;
+  }
+  return count;
+}
+
+
 void AssemblerBuffer::EmitObject(const Object& object) {
   // Since we are going to store the handle as part of the fixup information
   // the handle needs to be a zone handle.