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

src/wasm/module-decoder.cc

 // 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.
 
 #include "src/wasm/module-decoder.h"
 
 #include "src/base/functional.h"
 #include "src/base/platform/platform.h"
 #include "src/flags.h"
 #include "src/macro-assembler.h"
@@ skipping 1059 matching lines @@
     }
     decoder.consume_bytes(section_iter.payload_length(), "section payload");
     section_iter.advance();
   }
 
   return Vector<const uint8_t>();
 }
 
 }  // namespace
 
-ModuleResult DecodeWasmModule(Isolate* isolate, Zone* zone,
-                              const byte* module_start, const byte* module_end,
-                              bool verify_functions, ModuleOrigin origin) {
-  size_t decode_memory_start = zone->allocation_size();
+ModuleResult DecodeWasmModule(Isolate* isolate, const byte* module_start,
+                              const byte* module_end, bool verify_functions,
+                              ModuleOrigin origin) {
   HistogramTimerScope wasm_decode_module_time_scope(
       isolate->counters()->wasm_decode_module_time());
   size_t size = module_end - module_start;
   if (module_start > module_end) return ModuleError("start > end");
   if (size >= kMaxModuleSize) return ModuleError("size > maximum module size");
   // TODO(bradnelson): Improve histogram handling of size_t.
   isolate->counters()->wasm_module_size_bytes()->AddSample(
       static_cast<int>(size));
-  WasmModule* module = new WasmModule();
+  // Signatures are stored in zone memory, which have the same lifetime
+  // as the {module}.
+  Zone* zone = new Zone(isolate->allocator(), ZONE_NAME);
+  WasmModule* module = new WasmModule(zone, module_start);
   ModuleDecoder decoder(zone, module_start, module_end, origin);
   ModuleResult result = decoder.DecodeModule(module, verify_functions);
   // TODO(bradnelson): Improve histogram handling of size_t.
+  // TODO(titzer): this isn't accurate, since it doesn't count the data
+  // allocated on the C++ heap.
+  // https://bugs.chromium.org/p/chromium/issues/detail?id=657320
   isolate->counters()->wasm_decode_module_peak_memory_bytes()->AddSample(
-      static_cast<int>(zone->allocation_size() - decode_memory_start));
+      static_cast<int>(zone->allocation_size()));
   return result;
 }
 
 FunctionSig* DecodeWasmSignatureForTesting(Zone* zone, const byte* start,
                                            const byte* end) {
   ModuleDecoder decoder(zone, start, end, kWasmOrigin);
   return decoder.DecodeFunctionSignature(start);
 }
 
 WasmInitExpr DecodeWasmInitExprForTesting(const byte* start, const byte* end) {
@@ skipping 97 matching lines @@
     table.push_back(std::move(func_asm_offsets));
   }
   if (decoder.more()) decoder.error("unexpected additional bytes");
 
   return decoder.toResult(std::move(table));
 }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8