[WASM] Implements catch for the wasm low level exception mechanism.

src/runtime/runtime-wasm.cc

 // Copyright 2016 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/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/assembler.h"
 #include "src/compiler/wasm-compiler.h"
 #include "src/conversions.h"
@@ skipping 111 matching lines @@
   HandleScope scope(isolate);
   DCHECK_EQ(2, args.length());
   CONVERT_SMI_ARG_CHECKED(lower, 0);
   CONVERT_SMI_ARG_CHECKED(upper, 1);
 
   const int32_t thrown_value = (upper << 16) | lower;
 
   return isolate->Throw(*isolate->factory()->NewNumberFromInt(thrown_value));
 }
 
+RUNTIME_FUNCTION(Runtime_WasmGetCaughtExceptionValue) {
+  HandleScope scope(isolate);
+  DCHECK_EQ(1, args.length());
+  Object* exception = args[0];
+  // The unwinder will only deliver exceptions to wasm if the exception is a
+  // Number or a Smi (which we have just converted to a Number.) This logic
+  // lives in Isolate::is_catchable_by_wasm(Object*).
+  CHECK(exception->IsNumber());
+  return exception;
+}
+
 }  // namespace internal
 }  // namespace v8