Update dart2js parser to disallow repeated comparisons and prefix +.

sdk/lib/_internal/compiler/implementation/scanner/token.dart

Index: sdk/lib/_internal/compiler/implementation/scanner/token.dart
diff --git a/sdk/lib/_internal/compiler/implementation/scanner/token.dart b/sdk/lib/_internal/compiler/implementation/scanner/token.dart
index 81f6c8c12ee9499552b6e8d7239d43e455101190..bda4b762989a89c118a0a4b6e0759e23f272330f 100644
--- a/sdk/lib/_internal/compiler/implementation/scanner/token.dart
+++ b/sdk/lib/_internal/compiler/implementation/scanner/token.dart
@@ -431,28 +431,40 @@ const PrecedenceInfo AMPERSAND_INFO =
   const PrecedenceInfo(const SourceString('&'), 10, AMPERSAND_TOKEN);
 
 // Equality operators.
+const int EQUALITY_PRECEDENCE = 6;
 const PrecedenceInfo BANG_EQ_EQ_INFO =
-  const PrecedenceInfo(const SourceString('!=='), 6, BANG_EQ_EQ_TOKEN);
+  const PrecedenceInfo(const SourceString('!=='),
+                       EQUALITY_PRECEDENCE, BANG_EQ_EQ_TOKEN);
 const PrecedenceInfo BANG_EQ_INFO =
-  const PrecedenceInfo(const SourceString('!='), 6, BANG_EQ_TOKEN);
+  const PrecedenceInfo(const SourceString('!='),
+                       EQUALITY_PRECEDENCE, BANG_EQ_TOKEN);
 const PrecedenceInfo EQ_EQ_EQ_INFO =
-  const PrecedenceInfo(const SourceString('==='), 6, EQ_EQ_EQ_TOKEN);
+  const PrecedenceInfo(const SourceString('==='),
+                       EQUALITY_PRECEDENCE, EQ_EQ_EQ_TOKEN);
 const PrecedenceInfo EQ_EQ_INFO =
-  const PrecedenceInfo(const SourceString('=='), 6, EQ_EQ_TOKEN);
+  const PrecedenceInfo(const SourceString('=='),
+                       EQUALITY_PRECEDENCE, EQ_EQ_TOKEN);
 
 // Relational operators.
+const int RELATIONAL_PRECEDENCE = 7;
 const PrecedenceInfo GT_EQ_INFO =
-  const PrecedenceInfo(const SourceString('>='), 7, GT_EQ_TOKEN);
+  const PrecedenceInfo(const SourceString('>='),
+                       RELATIONAL_PRECEDENCE, GT_EQ_TOKEN);
 const PrecedenceInfo GT_INFO =
-  const PrecedenceInfo(const SourceString('>'), 7, GT_TOKEN);
+  const PrecedenceInfo(const SourceString('>'),
+                       RELATIONAL_PRECEDENCE, GT_TOKEN);
 const PrecedenceInfo IS_INFO =
-  const PrecedenceInfo(const SourceString('is'), 7, KEYWORD_TOKEN);
+  const PrecedenceInfo(const SourceString('is'),
+                       RELATIONAL_PRECEDENCE, KEYWORD_TOKEN);
 const PrecedenceInfo AS_INFO =
-  const PrecedenceInfo(const SourceString('as'), 7, KEYWORD_TOKEN);
+  const PrecedenceInfo(const SourceString('as'),
+                       RELATIONAL_PRECEDENCE, KEYWORD_TOKEN);
 const PrecedenceInfo LT_EQ_INFO =
-  const PrecedenceInfo(const SourceString('<='), 7, LT_EQ_TOKEN);
+  const PrecedenceInfo(const SourceString('<='),
+                       RELATIONAL_PRECEDENCE, LT_EQ_TOKEN);
 const PrecedenceInfo LT_INFO =
-  const PrecedenceInfo(const SourceString('<'), 7, LT_TOKEN);
+  const PrecedenceInfo(const SourceString('<'),
+                       RELATIONAL_PRECEDENCE, LT_TOKEN);
 
 // Shift operators.
 const PrecedenceInfo GT_GT_INFO =