[wasm] Require global names to be validate UTF-8.

R=ahaas@chromium.org,bradnelson@chromium.org
BUG=chromium:628542

Review-Url: https://codereview.chromium.org/2207183002
Cr-Commit-Position: refs/heads/master@{#38317}

src/wasm/module-decoder.cc

@@ -461,8 +461,10 @@ class ModuleDecoder : public Decoder {
   // Decodes a single global entry inside a module starting at {pc_}.
   void DecodeGlobalInModule(WasmGlobal* global) {
     global->name_offset = consume_string(&global->name_length, false);
-    DCHECK(unibrow::Utf8::Validate(start_ + global->name_offset,
-                                   global->name_length));
+    if (!unibrow::Utf8::Validate(start_ + global->name_offset,
+                                 global->name_length)) {
+      error("global name is not valid utf8");
+    }
     global->type = consume_local_type();
     global->offset = 0;
     global->exported = consume_u8("exported") != 0;