Added partially API-compatible database shim file for JS

Excluded methods:
1. `LDB() *leveldb.Database`
2. `NewIterator() iterator.Iterator`
3. `NewIteratorWithPrefix(prefix []byte) iterator.Iterator`

ethdb/database_js.go

@@ -0,0 +1,68 @@
+// Copyright 2014 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+// +build js
+
+package ethdb
+
+import (
+	"errors"
+)
+
+var errNotSupported = errors.New("ethdb: not supported")
+
+type LDBDatabase struct {
+}
+
+// NewLDBDatabase returns a LevelDB wrapped object.
+func NewLDBDatabase(file string, cache int, handles int) (*LDBDatabase, error) {
+	return nil, errNotSupported
+}
+
+// Path returns the path to the database directory.
+func (db *LDBDatabase) Path() string {
+	return ""
+}
+
+// Put puts the given key / value to the queue
+func (db *LDBDatabase) Put(key []byte, value []byte) error {
+	return errNotSupported
+}
+
+func (db *LDBDatabase) Has(key []byte) (bool, error) {
+	return false, errNotSupported
+}
+
+// Get returns the given key if it's present.
+func (db *LDBDatabase) Get(key []byte) ([]byte, error) {
+	return nil, errNotSupported
+}
+
+// Delete deletes the key from the queue and database
+func (db *LDBDatabase) Delete(key []byte) error {
+	return errNotSupported
+}
+
+func (db *LDBDatabase) Close() {
+}
+
+// Meter configures the database metrics collectors and
+func (db *LDBDatabase) Meter(prefix string) {
+}
+
+func (db *LDBDatabase) NewBatch() Batch {
+	return nil
+}