[wasm] Make sure the interpreter only executes preprocessed code.

BUG=chromium:646753
R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2365633002
Cr-Commit-Position: refs/heads/master@{#39638}

src/wasm/wasm-interpreter.cc

@@ -941,7 +941,7 @@ class CodeMap {
     if (function->func_index < interpreter_code_.size()) {
       InterpreterCode* code = &interpreter_code_[function->func_index];
       DCHECK_EQ(function, code->function);
-      return code;
+      return Preprocess(code);
     }
     return nullptr;
   }