[ddc] Escape type name identifiers

Avoids a compiler crash if invalid characters in the type names leak
from the CFE.

Change-Id: I3c9a9fcfd2ac6ef4f7ef5593a53d6f936653955e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/162260
Reviewed-by: Mark Zhou <markzipan@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>
diff --git a/pkg/dev_compiler/lib/src/kernel/type_table.dart b/pkg/dev_compiler/lib/src/kernel/type_table.dart
index 8421a66..8f8a002 100644
--- a/pkg/dev_compiler/lib/src/kernel/type_table.dart
+++ b/pkg/dev_compiler/lib/src/kernel/type_table.dart
@@ -123,7 +123,7 @@
   /// Heuristically choose a good name for the cache and generator
   /// variables.
   js_ast.TemporaryId chooseTypeName(DartType type) {
-    return js_ast.TemporaryId(_typeString(type));
+    return js_ast.TemporaryId(escapeIdentifier(_typeString(type)));
   }
 }