[wasm] Refactor encoder.h to use a proper buffer and remove OldFunctions section.

src/wasm/wasm-result.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/wasm-result.h"
 
 #include "src/factory.h"
 #include "src/heap/heap.h"
 #include "src/isolate.h"
 #include "src/objects-inl.h"  // TODO(mstarzinger): Temporary cycle breaker!
@@ skipping 11 matching lines @@
       os << "Success";
       break;
     default:  // TODO(titzer): render error codes
       os << "Error";
       break;
   }
   return os;
 }
 
 void ErrorThrower::Error(const char* format, ...) {
-  if (error_) return;  // only report the first error.
+  // only report the first error.
+  if (error_ || isolate_->has_pending_exception()) return;
   error_ = true;
   char buffer[256];
 
   va_list arguments;
   va_start(arguments, format);
   base::OS::VSNPrintF(buffer, 255, format, arguments);
   va_end(arguments);
 
   std::ostringstream str;
   if (context_ != nullptr) {
     str << context_ << ": ";
   }
   str << buffer;
 
   isolate_->ScheduleThrow(
       *isolate_->factory()->NewStringFromAsciiChecked(str.str().c_str()));
 }
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8