Cause `flutter analyze` to fail if the analysis server experienced an error. (#29126)

Substantially reduces the danger that a bug in the analysis server
might prevent errors from being detected by `flutter analyze`.

packages/flutter_tools/lib/src/commands/analyze_continuously.dart

@@ -67,6 +67,9 @@ class AnalyzeContinuously extends AnalyzeBase {
     if (exitCode != 0)
       throwToolExit(message, exitCode: exitCode);
     printStatus(message);
+
+    if (server.didServerErrorOccur)
+      throwToolExit('Server error(s) occurred.');
   }
 
   void _handleAnalysisStatus(AnalysisServer server, bool isAnalyzing) {

packages/flutter_tools/lib/src/commands/analyze_once.dart

@@ -155,6 +155,10 @@ class AnalyzeOnce extends AnalyzeBase {
       }
     }
 
+    if (server.didServerErrorOccur) {
+      throwToolExit('Server error(s) occurred. (ran in ${seconds}s)');
+    }
+
     if (argResults['congratulate']) {
       if (undocumentedMembers > 0) {
         printStatus('No issues found! (ran in ${seconds}s; $dartdocMessage)');

packages/flutter_tools/lib/src/dart/analysis.dart

@@ -27,6 +27,7 @@ class AnalysisServer {
       StreamController<bool>.broadcast();
   final StreamController<FileAnalysisErrors> _errorsController =
       StreamController<FileAnalysisErrors>.broadcast();
+  bool _didServerErrorOccur = false;
 
   int _id = 0;
 
@@ -61,6 +62,7 @@ class AnalysisServer {
         <String, dynamic>{'included': directories, 'excluded': <String>[]});
   }
 
+  bool get didServerErrorOccur => _didServerErrorOccur;
   Stream<bool> get onAnalyzing => _analyzingController.stream;
   Stream<FileAnalysisErrors> get onErrors => _errorsController.stream;
 
@@ -120,6 +122,7 @@ class AnalysisServer {
     if (error['stackTrace'] != null) {
       printError(error['stackTrace']);
     }
+    _didServerErrorOccur = true;
   }
 
   void _handleAnalysisIssues(Map<String, dynamic> issueInfo) {