Use limited JavaStringBuilder implementation instead of Dart StringBuffer.

pkg/analyzer-experimental/lib/src/generated/java_core.dart

Index: pkg/analyzer-experimental/lib/src/generated/java_core.dart
diff --git a/pkg/analyzer-experimental/lib/src/generated/java_core.dart b/pkg/analyzer-experimental/lib/src/generated/java_core.dart
index a450fbd85de638cc6afdb9fe190f37f7403ca222..7119161c4ca76e929f4ddb4570189b6fdac821bd 100644
--- a/pkg/analyzer-experimental/lib/src/generated/java_core.dart
+++ b/pkg/analyzer-experimental/lib/src/generated/java_core.dart
@@ -390,3 +390,22 @@ void javaMapPutAll(Map target, Map source) {
 bool javaStringEqualsIgnoreCase(String a, String b) {
   return a.toLowerCase() == b.toLowerCase();
 }
+
+class JavaStringBuilder {
+  StringBuffer sb = new StringBuffer();
+  String toString() => sb.toString();
+  void append(x) {
+    sb.write(x);
+  }
+  void appendChar(int c) {
+    sb.writeCharCode(c);
+  }
+  int get length => sb.length;
+  void set length(int len) {
+    var s = sb.toString().substring(0, len);
+    sb = new StringBuffer(s);
+  }
+  void clear() {
+    sb = new StringBuffer();
+  }
+}