Add a CHECK for null stuff in CompactPendingRules

This should be impossible, but we'd like to try it in canary
to try and figure out what's going on in the linked bug.

This should be reverted by 17 March.

BUG=694520

Review-Url: https://codereview.chromium.org/2740013002
Cr-Commit-Position: refs/heads/master@{#455697}

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

@@ -350,8 +350,13 @@ void RuleSet::compactPendingRules(PendingRuleMap& pendingMap,
                                   CompactRuleMap& compactMap) {
   for (auto& item : pendingMap) {
     HeapLinkedStack<RuleData>* pendingRules = item.value.release();
+    // TODO(meade): crbug.com/694520
+    CHECK(!item.key.isNull());
+    CHECK(pendingRules);
     CompactRuleMap::ValueType* compactRules =
         compactMap.insert(item.key, nullptr).storedValue;
+    // TODO(meade): crbug.com/694520
+    CHECK(compactRules);
 
     HeapTerminatedArrayBuilder<RuleData> builder(compactRules->value.release());
     builder.grow(pendingRules->size());
@@ -365,7 +370,8 @@ void RuleSet::compactPendingRules(PendingRuleMap& pendingMap,
 }
 
 void RuleSet::compactRules() {
-  ASSERT(m_pendingRules);
+  // TODO(meade): crbug.com/694520
+  CHECK(m_pendingRules);
   PendingRuleMaps* pendingRules = m_pendingRules.release();
   compactPendingRules(pendingRules->idRules, m_idRules);
   compactPendingRules(pendingRules->classRules, m_classRules);