ARM: don't use r9 anymore for gap resolution

src/arm/lithium-gap-resolver-arm.h

Index: src/arm/lithium-gap-resolver-arm.h
diff --git a/src/arm/lithium-gap-resolver-arm.h b/src/arm/lithium-gap-resolver-arm.h
index 044c2864a42e695ca12e29c931d7c5ccb7bd5bfd..066f880b935e96f7c5fc916af9c7997fe45eacce 100644
--- a/src/arm/lithium-gap-resolver-arm.h
+++ b/src/arm/lithium-gap-resolver-arm.h
@@ -76,6 +76,10 @@ class LGapResolver V8_FINAL BASE_EMBEDDED {
   int root_index_;
   bool in_cycle_;
   LOperand* saved_destination_;
+
+  // We use the root register as a scratch in a few places. When that happens,
+  // this flag is set to indicate that it needs to be restored.
+  bool need_to_restore_root_;
 };
 
 } }  // namespace v8::internal