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

src/wasm/ast-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_AST_DECODER_H_
 #define V8_WASM_AST_DECODER_H_
 
 #include "src/signature.h"
 #include "src/wasm/decoder.h"
 #include "src/wasm/wasm-opcodes.h"
@@ skipping 202 matching lines @@
                                const byte* end) {
   FunctionBody body = {module, sig, nullptr, start, end};
   return BuildTFGraph(allocator, builder, body);
 }
 
 enum ReadUnsignedLEB128ErrorCode { kNoError, kInvalidLEB128, kMissingLEB128 };
 
 ReadUnsignedLEB128ErrorCode ReadUnsignedLEB128Operand(const byte*, const byte*,
                                                       int*, uint32_t*);
 
-std::vector<LocalType>* DecodeLocalDeclsForTesting(
-    base::AccountingAllocator* allocator, const byte* start, const byte* end);
+struct AstLocalDecls {
+  // The size of the encoded declarations.
+  uint32_t decls_encoded_size;  // size of encoded declarations
+
+  // Total number of locals.
+  uint32_t total_local_count;
+
+  // List of {local type, count} pairs.
+  ZoneVector<std::pair<LocalType, uint32_t>> local_types;
+
+  // Constructor initializes the vector.
+  explicit AstLocalDecls(Zone* zone)
+      : decls_encoded_size(0), total_local_count(0), local_types(zone) {}
+};
+
+bool DecodeLocalDecls(AstLocalDecls& decls, const byte* start, const byte* end);
 BitVector* AnalyzeLoopAssignmentForTesting(Zone* zone, size_t num_locals,
                                            const byte* start, const byte* end);
 
 // Computes the length of the opcode at the given address.
 int OpcodeLength(const byte* pc, const byte* end);
 
 // Computes the arity (number of sub-nodes) of the opcode at the given address.
 int OpcodeArity(ModuleEnv* module, FunctionSig* sig, const byte* pc,
                 const byte* end);
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_AST_DECODER_H_