[turbofan] Introduce an ExternalPointer type.

src/compiler/js-graph.h

Index: src/compiler/js-graph.h
diff --git a/src/compiler/js-graph.h b/src/compiler/js-graph.h
index d5d3daf6f8075c5b56f2074693cd56153c60af22..c2c0c77f42b0e44251c317c8b73521bf60c55350 100644
--- a/src/compiler/js-graph.h
+++ b/src/compiler/js-graph.h
@@ -108,10 +108,6 @@ class V8_EXPORT_PRIVATE JSGraph : public NON_EXPORTED_BASE(ZoneObject) {
     return machine()->Is32() ? Int32Constant(static_cast<int32_t>(value))
                              : Int64Constant(static_cast<int64_t>(value));
   }
-  template <typename T>
-  Node* PointerConstant(T* value) {
-    return IntPtrConstant(bit_cast<intptr_t>(value));
-  }
 
   Node* RelocatableInt32Constant(int32_t value, RelocInfo::Mode rmode);
   Node* RelocatableInt64Constant(int64_t value, RelocInfo::Mode rmode);
@@ -123,6 +119,13 @@ class V8_EXPORT_PRIVATE JSGraph : public NON_EXPORTED_BASE(ZoneObject) {
   // Creates a Float64Constant node, usually canonicalized.
   Node* Float64Constant(double value);
 
+  // Creates a PointerConstant node (asm.js only).
+  Node* PointerConstant(intptr_t value);
+  template <typename T>
+  Node* PointerConstant(T* value) {
+    return PointerConstant(bit_cast<intptr_t>(value));
+  }
+
   // Creates an ExternalConstant node, usually canonicalized.
   Node* ExternalConstant(ExternalReference ref);
   Node* ExternalConstant(Runtime::FunctionId function_id);