[Interpreter] Ensure that implicit return undefined is generated.

src/interpreter/bytecode-generator.cc

Index: src/interpreter/bytecode-generator.cc
diff --git a/src/interpreter/bytecode-generator.cc b/src/interpreter/bytecode-generator.cc
index 487b86543794b9effc862db130ea37a2e0e36ca7..0f24995c92a9b150b38f002a73ea5d70ff61a360 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -45,6 +45,13 @@ Handle<BytecodeArray> BytecodeGenerator::MakeBytecode(CompilationInfo* info) {
   // Visit statements in the function body.
   VisitStatements(info->literal()->body());
 
+  // If the last bytecode wasn't a return, then return 'undefined' to avoid
+  // falling off the end.
+  if (!builder_.HasExplicitReturn()) {
+    builder_.LoadUndefined();
+    builder_.Return();
+  }
+
   set_scope(nullptr);
   set_info(nullptr);
   return builder_.ToBytecodeArray();