fix(#7099): support for comment finishing with multiple dashes

<!-- xxxx ------->

The issue came from a lack of support for backtracking on string
matching.
The way it is done, if the "end pattern" for consumeRawText starts with
twice the same character, you end up having problem when your string
being parsed has 3 times this char

Example
End string: xxyz
string to parse: aaaaaaxxxyz

calling consumeRawText(false, 'x', attemptParseStr('xyz')) would fail

Closes #7119

modules/@angular/compiler/src/html_lexer.ts

@@ -267,8 +267,16 @@ class _HtmlTokenizer {
   }
 
   private _attemptStr(chars: string): boolean {
+    var indexBeforeAttempt = this.index;
+    var columnBeforeAttempt = this.column;
+    var lineBeforeAttempt = this.line;
     for (var i = 0; i < chars.length; i++) {
       if (!this._attemptCharCode(StringWrapper.charCodeAt(chars, i))) {
+        // If attempting to parse the string fails, we want to reset the parser
+        // to where it was before the attempt
+        this.index = indexBeforeAttempt;
+        this.column = columnBeforeAttempt;
+        this.line = lineBeforeAttempt;
         return false;
       }
     }