Make catch variables final.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index aded0f24e94f9df966a9c5c68e2c43067a04222c..5b1ad433d2eb734c540649ff2bd79604b94df9a9 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -1393,7 +1393,12 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
     }
     Identifier name = pop();
     DartType type = pop();
-    pop(); // Modifiers.
+    int modifiers = Modifier.validate(pop());
+    if (inCatchClause) {
+      modifiers |= finalMask;
+    }
+    bool isConst = (modifiers & constMask) != 0;
+    bool isFinal = (modifiers & finalMask) != 0;
     ignore(Unhandled.Metadata);
     VariableDeclaration variable;
     if (!inCatchClause && functionNestingLevel == 0) {
@@ -1417,7 +1422,10 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
         }
         type = field.target.type ?? const DynamicType();
         variable = new VariableDeclaration(name.name,
-            type: type, initializer: name.initializer);
+            type: type,
+            initializer: name.initializer,
+            isFinal: isFinal,
+            isConst: isConst)..fileOffset = name.fileOffset;
       } else {
         addCompileTimeError(
             name.fileOffset, "'${name.name}' isn't a field in this class.");
@@ -1425,7 +1433,9 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
     }
     variable ??= new VariableDeclaration(name.name,
         type: type ?? const DynamicType(),
-        initializer: name.initializer)..fileOffset = name.fileOffset;
+        initializer: name.initializer,
+        isFinal: isFinal,
+        isConst: isConst)..fileOffset = name.fileOffset;
     push(variable);
   }