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

src/runtime/runtime-wasm.cc

Index: src/runtime/runtime-wasm.cc
diff --git a/src/runtime/runtime-wasm.cc b/src/runtime/runtime-wasm.cc
index d41be53a4e365f3ffb90bdcf16790534a4251fae..0662f3d7089727692975499aa7da068694ec166f 100644
--- a/src/runtime/runtime-wasm.cc
+++ b/src/runtime/runtime-wasm.cc
@@ -129,5 +129,16 @@ RUNTIME_FUNCTION(Runtime_WasmThrow) {
   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