Collect media query results for non-matching stylesheets.

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/css/ActiveStyleSheets.h"
 
 #include "core/css/CSSStyleSheet.h"
 #include "core/css/RuleSet.h"
 #include "core/css/resolver/ScopedStyleResolver.h"
 #include "core/dom/ContainerNode.h"
@@ skipping 19 matching lines @@
        index++) {
     if (new_style_sheets[index].second == old_style_sheets[index].second)
       continue;
 
     if (new_style_sheets[index].second)
       changed_rule_sets.insert(new_style_sheets[index].second);
     if (old_style_sheets[index].second)
       changed_rule_sets.insert(old_style_sheets[index].second);
   }
 
+  // If we add a sheet for which the media attribute currently doesn't match, we
+  // have a null RuleSet and there's no need to do any style invalidation.
+  // However, we need to tell the StyleEngine to re-collect viewport and device
+  // dependent media query results so that we can correctly update active style
+  // sheets when such media query evaluations change.
+  bool adds_non_matching_mq = false;
+
   if (index == old_style_sheet_count) {
     // The old stylesheet vector is a prefix of the new vector in terms of
     // StyleSheets. If none of the RuleSets changed, we only need to add the new
     // sheets to the ScopedStyleResolver (ActiveSheetsAppended).
     bool rule_sets_changed_in_common_prefix = !changed_rule_sets.IsEmpty();
     for (; index < new_style_sheet_count; index++) {
       if (new_style_sheets[index].second)
         changed_rule_sets.insert(new_style_sheets[index].second);
+      else if (new_style_sheets[index].first->HasMediaQueryResults())
+        adds_non_matching_mq = true;
     }
     if (rule_sets_changed_in_common_prefix)
       return kActiveSheetsChanged;
-    if (changed_rule_sets.IsEmpty())
+    if (changed_rule_sets.IsEmpty() && !adds_non_matching_mq)
       return kNoActiveSheetsChanged;
     return kActiveSheetsAppended;
   }
 
   if (index == new_style_sheet_count) {
     // Sheets removed from the end.
     for (; index < old_style_sheet_count; index++) {
       if (old_style_sheets[index].second)
         changed_rule_sets.insert(old_style_sheets[index].second);
+      else if (old_style_sheets[index].first->HasMediaQueryResults())
+        adds_non_matching_mq = true;
     }
-    return changed_rule_sets.IsEmpty() ? kNoActiveSheetsChanged
-                                       : kActiveSheetsChanged;
+    return changed_rule_sets.IsEmpty() && !adds_non_matching_mq
+               ? kNoActiveSheetsChanged
+               : kActiveSheetsChanged;
   }
 
   DCHECK_LT(index, old_style_sheet_count);
   DCHECK_LT(index, new_style_sheet_count);
 
   // Both the new and old active stylesheet vectors have stylesheets following
   // the common prefix. Figure out which were added or removed by sorting the
   // merged vector of old and new sheets.
 
   ActiveStyleSheetVector merged_sorted;
   merged_sorted.ReserveCapacity(old_style_sheet_count + new_style_sheet_count -
                                 2 * index);
   merged_sorted.AppendRange(old_style_sheets.begin() + index,
                             old_style_sheets.end());
   merged_sorted.AppendRange(new_style_sheets.begin() + index,
                             new_style_sheets.end());
 
   std::sort(merged_sorted.begin(), merged_sorted.end());
 
   auto merged_iterator = merged_sorted.begin();
   while (merged_iterator != merged_sorted.end()) {
     const auto& sheet1 = *merged_iterator++;
     if (merged_iterator == merged_sorted.end() ||
         (*merged_iterator).first != sheet1.first) {
       // Sheet either removed or inserted.
       if (sheet1.second)
         changed_rule_sets.insert(sheet1.second);
+      else if (sheet1.first->HasMediaQueryResults())
+        adds_non_matching_mq = true;
       continue;
     }
 
     // Sheet present in both old and new.
     const auto& sheet2 = *merged_iterator++;
 
     if (sheet1.second == sheet2.second)
       continue;
 
     // Active rules for the given stylesheet changed.
     // DOM, CSSOM, or media query changes.
     if (sheet1.second)
       changed_rule_sets.insert(sheet1.second);
     if (sheet2.second)
       changed_rule_sets.insert(sheet2.second);
   }
-  return changed_rule_sets.IsEmpty() ? kNoActiveSheetsChanged
-                                     : kActiveSheetsChanged;
+  return changed_rule_sets.IsEmpty() && !adds_non_matching_mq
+             ? kNoActiveSheetsChanged
+             : kActiveSheetsChanged;
 }
 
 }  // namespace blink