Improve error messages for invalid requests

pkg/analysis_server/tool/spec/codegen_dart_protocol.dart

Index: pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
diff --git a/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart b/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
index 88df36bd6cbdd5d0feb47504f75e2c4545486ab1..755ed526cebae56e4a06f71f0919b3b3423a23c1 100644
--- a/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
+++ b/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
@@ -349,7 +349,7 @@ class CodegenProtocolVisitor extends DartCodegenVisitor with CodeGenerator {
       String humanReadableNameString =
           literalString(impliedType.humanReadableName);
       writeln(
-          'throw jsonDecoder.mismatch(jsonPath, $humanReadableNameString);');
+          'throw jsonDecoder.mismatch(jsonPath, $humanReadableNameString, json);');
     });
     writeln('}');
   }
@@ -590,7 +590,7 @@ class CodegenProtocolVisitor extends DartCodegenVisitor with CodeGenerator {
             writeln('if ($fieldAccessor != $valueString) {');
             indent(() {
               writeln(
-                  'throw jsonDecoder.mismatch(jsonPath, "equal " + $valueString);');
+                  'throw jsonDecoder.mismatch(jsonPath, "equal " + $valueString, json);');
             });
             writeln('}');
             continue;
@@ -627,7 +627,7 @@ class CodegenProtocolVisitor extends DartCodegenVisitor with CodeGenerator {
       writeln('} else {');
       indent(() {
         writeln(
-            'throw jsonDecoder.mismatch(jsonPath, $humanReadableNameString);');
+            'throw jsonDecoder.mismatch(jsonPath, $humanReadableNameString, json);');
       });
       writeln('}');
     });