Fix a FindBugs warning in JsonSanitizer.java

components/safe_json/android/java/src/org/chromium/components/safejson/JsonSanitizer.java

Index: components/safe_json/android/java/src/org/chromium/components/safejson/JsonSanitizer.java
diff --git a/components/safe_json/android/java/src/org/chromium/components/safejson/JsonSanitizer.java b/components/safe_json/android/java/src/org/chromium/components/safejson/JsonSanitizer.java
index 50da4b0fdfc34fd18cad7e89cfdf57f390e00477..9ab07a7c762d0a40aeb43777525153671d78a68b 100644
--- a/components/safe_json/android/java/src/org/chromium/components/safejson/JsonSanitizer.java
+++ b/components/safe_json/android/java/src/org/chromium/components/safejson/JsonSanitizer.java
@@ -99,6 +99,8 @@ public class JsonSanitizer {
                     case END_DOCUMENT:
                         end = true;
                         break;
+                    default:
+                        assert false : token;
                 }
             }
             result = stringWriter.toString();