AAPT2: Accept Java unicode identifiers

Test: make aapt2_tests
Change-Id: I75a0e52d43b1785001bfe120eea7484f7bb4682b
diff --git a/tools/aapt2/text/Utf8Iterator.cpp b/tools/aapt2/text/Utf8Iterator.cpp
new file mode 100644
index 0000000..0d43353
--- /dev/null
+++ b/tools/aapt2/text/Utf8Iterator.cpp
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "text/Utf8Iterator.h"
+
+#include "android-base/logging.h"
+#include "utils/Unicode.h"
+
+using ::android::StringPiece;
+
+namespace aapt {
+namespace text {
+
+Utf8Iterator::Utf8Iterator(const StringPiece& str)
+    : str_(str), next_pos_(0), current_codepoint_(0) {
+  DoNext();
+}
+
+void Utf8Iterator::DoNext() {
+  size_t next_pos = 0u;
+  int32_t result = utf32_from_utf8_at(str_.data(), str_.size(), next_pos_, &next_pos);
+  if (result == -1) {
+    current_codepoint_ = 0u;
+  } else {
+    current_codepoint_ = static_cast<char32_t>(result);
+    next_pos_ = next_pos;
+  }
+}
+
+bool Utf8Iterator::HasNext() const {
+  return current_codepoint_ != 0;
+}
+
+void Utf8Iterator::Skip(int amount) {
+  while (amount > 0 && HasNext()) {
+    Next();
+    --amount;
+  }
+}
+
+char32_t Utf8Iterator::Next() {
+  CHECK(HasNext()) << "Next() called after iterator exhausted";
+  char32_t result = current_codepoint_;
+  DoNext();
+  return result;
+}
+
+}  // namespace text
+}  // namespace aapt