[wasm] Use a Managed<WasmModule> to hold metadata about modules.

src/signature.h

Index: src/signature.h
diff --git a/src/signature.h b/src/signature.h
index 97238b6749fbb82a05562a9c5ea2f30a97115db7..32050fe4b0178476d296672ba8fe8dee6dd41a52 100644
--- a/src/signature.h
+++ b/src/signature.h
@@ -32,7 +32,16 @@ class Signature : public ZoneObject {
     return reps_[index];
   }
 
-  const T* raw_data() const { return reps_; }
+  bool Equals(Signature* that) {
+    if (this == that) return true;
+    if (this->parameter_count() != that->parameter_count()) return false;
+    if (this->return_count() != that->return_count()) return false;
+    size_t size = this->return_count() + this->parameter_count();
+    for (size_t i = 0; i < size; i++) {
+      if (this->reps_[i] != that->reps_[i]) return false;
+    }
+    return true;
+  }
 
   // For incrementally building signatures.
   class Builder {