[wasm][asm.js] Check if a property key is a PropertyName before assumming it.

src/asmjs/asm-typer.cc

Index: src/asmjs/asm-typer.cc
diff --git a/src/asmjs/asm-typer.cc b/src/asmjs/asm-typer.cc
index 2389551872a8b5e5f63e0da907b1a4aeff1e3f86..503bbaee398f667c68c58317a4a41efa9ae657cb 100644
--- a/src/asmjs/asm-typer.cc
+++ b/src/asmjs/asm-typer.cc
@@ -385,6 +385,10 @@ AsmTyper::VariableInfo* AsmTyper::ImportLookup(Property* import) {
     return obj_info;
   }
 
+  if (!key->IsPropertyName()) {
+    return nullptr;
+  }
+
   std::unique_ptr<char[]> aname = key->AsPropertyName()->ToCString();
   ObjectTypeMap::iterator i = stdlib->find(std::string(aname.get()));
   if (i == stdlib->end()) {