Validate that root paths are absolute and normalized.

pkg/analysis_server/lib/src/analysis_server.dart

Index: pkg/analysis_server/lib/src/analysis_server.dart
diff --git a/pkg/analysis_server/lib/src/analysis_server.dart b/pkg/analysis_server/lib/src/analysis_server.dart
index 980bb9de7126387e6081e6a95045a54b05220d0c..f72f051e2077cad3b693bd2d28a4b37564ffc451 100644
--- a/pkg/analysis_server/lib/src/analysis_server.dart
+++ b/pkg/analysis_server/lib/src/analysis_server.dart
@@ -185,8 +185,8 @@ class AnalysisServer {
    * A table mapping [AnalysisContext]s to the completers that should be
    * completed when analysis of this context is finished.
    */
-  Map<AnalysisContext,
-          Completer<AnalysisDoneReason>> contextAnalysisDoneCompleters =
+  Map<AnalysisContext, Completer<AnalysisDoneReason>>
+      contextAnalysisDoneCompleters =
       new HashMap<AnalysisContext, Completer<AnalysisDoneReason>>();
 
   /**
@@ -732,6 +732,15 @@ class AnalysisServer {
   }
 
   /**
+   * Return `true` if the given path is a valid `FilePath`.
+   *
+   * This means that it is absolute and normalized.
+   */
+  bool isValidFilePath(String path) {
+    return resourceProvider.absolutePathContext.isValid(path);
+  }
+
+  /**
    * Returns a [Future] completing when [file] has been completely analyzed, in
    * particular, all its errors have been computed.  The future is completed
    * with an [AnalysisDoneReason] indicating what caused the file's analysis to