Bug 1382023 - Fold repeated assertions. r=jandem

This is a pull of v8 commit c8e4c8b9263b5009716804f06f39225a9dd7fc68,
reviewed at https://codereview.chromium.org/2768443003.

--HG--
extra : histedit_source : a18886aba3443d84eb909f1f37a3d63b7aa415a9

js/src/irregexp/RegExpParser.cpp

@@ -129,6 +129,12 @@ void
 RegExpBuilder::AddAssertion(RegExpTree* assert)
 {
     FlushText();
+    if (terms_.length() > 0 && terms_.last()->IsAssertion()) {
+        // Omit repeated assertions of the same type.
+        RegExpAssertion* last = terms_.last()->AsAssertion();
+        RegExpAssertion* next = assert->AsAssertion();
+        if (last->assertion_type() == next->assertion_type()) return;
+    }
     terms_.Add(alloc, assert);
 #ifdef DEBUG
     last_added_ = ADD_ASSERT;