[wasm] Refactor decoding of local declarations and make more robust.

src/wasm/decoder.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_WASM_DECODER_H_
 #define V8_WASM_DECODER_H_
 
 #include "src/base/smart-pointers.h"
 #include "src/flags.h"
 #include "src/signature.h"
@@ skipping 311 matching lines @@
     start_ = start;
     pc_ = start;
     limit_ = end;
     end_ = end;
     error_pc_ = nullptr;
     error_pt_ = nullptr;
     error_msg_.Reset(nullptr);
   }
 
   bool ok() const { return error_pc_ == nullptr; }
-  bool failed() const { return error_pc_ != nullptr; }
+  bool failed() const { return !error_msg_.is_empty(); }
   bool more() const { return pc_ < limit_; }
 
   const byte* start() { return start_; }
   const byte* pc() { return pc_; }
   uint32_t pc_offset() { return static_cast<uint32_t>(pc_ - start_); }
 
  protected:
   const byte* start_;
   const byte* pc_;
   const byte* limit_;
@@ skipping 56 matching lines @@
     return result;
   }
 };
 
 #undef TRACE
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_DECODER_H_