[parsing] Update the comment on BuildUnaryExpression.

R=adamk@chromium.org

Bug: 
Change-Id: Ic5668ba70065c7315c354b9921b3c493080da2a7
Reviewed-on: https://chromium-review.googlesource.com/803254Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49812}

src/parsing/parser.h

@@ -760,17 +760,11 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
   bool CollapseNaryExpression(Expression** x, Expression* y, Token::Value op,
                               int pos, const SourceRange& range);
 
-  // Rewrites the following types of unary expressions:
-  // not <literal> -> true / false
-  // + <numeric literal> -> <numeric literal>
-  // - <numeric literal> -> <numeric literal with value negated>
+  // Returns a UnaryExpression or, in one of the following cases, a Literal.
   // ! <literal> -> true / false
-  // The following rewriting rules enable the collection of type feedback
-  // without any special stub and the multiplication is removed later in
-  // Crankshaft's canonicalization pass.
-  // + foo -> foo * 1
-  // - foo -> foo * (-1)
-  // ~ foo -> foo ^(~0)
+  // + <Number literal> -> <Number literal>
+  // - <Number literal> -> <Number literal with value negated>
+  // ~ <literal> -> true / false
   Expression* BuildUnaryExpression(Expression* expression, Token::Value op,
                                    int pos);