Reduce impact of HParameter inputs on HPhi representation selection

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index b933f10ba80f266d67f3ead95ca21a42ee43f216..800fa49a326d9b730ecd7d17c39ddaaa68b1c684 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -1641,6 +1641,11 @@ class HForceRepresentation FINAL : public HTemplateInstruction<1> {
 
   HValue* value() const { return OperandAt(0); }
 
+  Representation observed_input_representation(int index) OVERRIDE {
+    // We haven't actually *observed* this, but it's closer to the truth
+    // than 'None'.
+    return representation();  // Same as the output representation.
+  }
   Representation RequiredInputRepresentation(int index) OVERRIDE {
     return representation();  // Same as the output representation.
   }