Introduce element categories and move resolver towards being more compositional.

dart/frog/leg/scanner/parser.dart

Index: dart/frog/leg/scanner/parser.dart
diff --git a/dart/frog/leg/scanner/parser.dart b/dart/frog/leg/scanner/parser.dart
index 0c526e90dddd018511720e56f2d8a7e772d83333..72304cdd9a8fa8cf379341531e495afe8783489f 100644
--- a/dart/frog/leg/scanner/parser.dart
+++ b/dart/frog/leg/scanner/parser.dart
@@ -657,7 +657,7 @@ class Parser {
 
   Token parseOperatorName(Token token) {
     assert(optional('operator', token));
-    if (isUserDefinableOperator(token.next)) {
+    if (isUserDefinableOperator(token.next.stringValue)) {
       Token operator = token;
       token = token.next;
       listener.handleOperatorName(operator, token);
@@ -667,32 +667,6 @@ class Parser {
     }
   }
 
-  bool isUserDefinableOperator(Token token) {
-    String value = token.stringValue;
-    return
-      (value === '==') ||
-      (value === '~') ||
-      (value === 'negate') ||
-      (value === '[]') ||
-      (value === '[]=') ||
-      (value === '*') ||
-      (value === '/') ||
-      (value === '%') ||
-      (value === '~/') ||
-      (value === '+') ||
-      (value === '-') ||
-      (value === '<<') ||
-      (value === '>>>') ||
-      (value === '>>') ||
-      (value === '>=') ||
-      (value === '>') ||
-      (value === '<=') ||
-      (value === '<') ||
-      (value === '&') ||
-      (value === '^') ||
-      (value === '|');
-  }
-
   Token parseFunction(Token token, Token getOrSet) {
     listener.beginFunction(token);
     token = parseModifiers(token);