Rename `LazyString` to `OnDemandString` since the concept of "laziness" usually implies caching.

PiperOrigin-RevId: 379556596
diff --git a/src/main/java/com/google/devtools/build/lib/util/OnDemandString.java b/src/main/java/com/google/devtools/build/lib/util/OnDemandString.java
new file mode 100644
index 0000000..a14edf5
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/util/OnDemandString.java
@@ -0,0 +1,38 @@
+// Copyright 2014 The Bazel Authors. All rights reserved.
+//
+// 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.
+
+package com.google.devtools.build.lib.util;
+
+/**
+ * This class serves as a base implementation for a {@code CharSequence}
+ * that delays string construction (mostly till the execution phase).
+ */
+public abstract class OnDemandString implements CharSequence {
+
+  @Override
+  public char charAt(int index) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public int length() {
+    return toString().length();
+  }
+
+  @Override
+  public CharSequence subSequence(int start, int end) {
+    throw new UnsupportedOperationException();
+  }
+
+}