Ignore any selectors at index 8192 or beyond

Since the selector index field in RuleData is only 13 bits, we can only
support lookups in the range 0-8191. We must ignore any selectors
outside this range.

BUG=804179,632009

Change-Id: I11c0acfe27813d98f24f72fb7e50f13b326a0e84
Reviewed-on: https://chromium-review.googlesource.com/883702Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Manish Jethani <m.jethani@eyeo.com>
Cr-Commit-Position: refs/heads/master@{#531931}

third_party/WebKit/Source/core/css/RuleSet.cpp

@@ -222,6 +222,11 @@ bool RuleSet::FindBestRuleSetAndAdd(const CSSSelector& component,
 void RuleSet::AddRule(StyleRule* rule,
                       unsigned selector_index,
                       AddRuleFlags add_rule_flags) {
+  // The selector index field in RuleData is only 13 bits so we can't support
+  // selectors at index 8192 or beyond.
+  // See https://crbug.com/804179
+  if (selector_index >= 8192)
+    return;
   RuleData rule_data(rule, selector_index, rule_count_++, add_rule_flags);
   if (features_.CollectFeaturesFromRuleData(rule_data) ==
       RuleFeatureSet::kSelectorNeverMatches)