Cache element docs (and add to completions) (#23694).

pkg/analysis_server/lib/src/utilities/documentation.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library analysis_server.src.utilities.documentation;
+
+String getDartDocSummary(String str) {
+  if (str == null) {
+    return null;
+  }
+  List<String> lines = str.split('\n');
+  StringBuffer sb = new StringBuffer();
+  bool firstLine = true;
+  for (String line in lines) {
+    if (sb.length != 0 && line.isEmpty) {
+      return sb.toString();
+    }
+    if (!firstLine) {
+      sb.write('\n');
+    }
+    firstLine = false;
+    sb.write(line);
+  }
+  return sb.toString();
+}
+
+/**
+ * Converts [str] from a Dart Doc string with slashes and stars to a plain text
+ * representation of the comment.
+ */
+String removeDartDocDelimiters(String str) {
+  if (str == null) {
+    return null;
+  }
+  // remove /** */
+  if (str.startsWith('/**')) {
+    str = str.substring(3);
+  }
+  if (str.endsWith("*/")) {
+    str = str.substring(0, str.length - 2);
+  }
+  str = str.trim();
+  // remove leading '* ' and '/// '
+  List<String> lines = str.split('\n');
+  StringBuffer sb = new StringBuffer();
+  bool firstLine = true;
+  for (String line in lines) {
+    line = line.trim();
+    if (line.startsWith("*")) {
+      line = line.substring(1);
+      if (line.startsWith(" ")) {
+        line = line.substring(1);
+      }
+    } else if (line.startsWith("///")) {
+      line = line.substring(3);
+      if (line.startsWith(" ")) {
+        line = line.substring(1);
+      }
+    }
+    if (!firstLine) {
+      sb.write('\n');
+    }
+    firstLine = false;
+    sb.write(line);
+  }
+  str = sb.toString();
+  // done
+  return str;
+}