From 6e3f0feaaaf60957714d40c46f48941e59cf1e32 Mon Sep 17 00:00:00 2001
From: Cameron McCormack <cam>
Date: Mon, 24 Oct 2016 02:59:00 +0200
Subject: [PATCH] Bug 1312331 - Build up list of applicable rules in reverse to
 avoid quadratic time array manipulations. r=erahm

MozReview-Commit-ID: HAjtxQVZo8X
---
 layout/inspector/inDOMUtils.cpp | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/layout/inspector/inDOMUtils.cpp b/layout/inspector/inDOMUtils.cpp
index adc1525b2899..9f1dcaad3fc8 100644
--- a/layout/inspector/inDOMUtils.cpp
+++ b/layout/inspector/inDOMUtils.cpp
@@ -247,8 +247,14 @@ inDOMUtils::GetCSSStyleRules(nsIDOMElement *aElement,
     return NS_OK;
   }
 
+  AutoTArray<nsRuleNode*, 16> ruleNodes;
+  while (!ruleNode->IsRoot()) {
+    ruleNodes.AppendElement(ruleNode);
+    ruleNode = ruleNode->GetParent();
+  }
+
   nsCOMPtr<nsIMutableArray> rules = nsArray::Create();
-  for ( ; !ruleNode->IsRoot(); ruleNode = ruleNode->GetParent()) {
+  for (nsRuleNode* ruleNode : Reversed(ruleNodes)) {
     RefPtr<Declaration> decl = do_QueryObject(ruleNode->GetRule());
     if (decl) {
       RefPtr<mozilla::css::StyleRule> styleRule =
@@ -256,7 +262,7 @@ inDOMUtils::GetCSSStyleRules(nsIDOMElement *aElement,
       if (styleRule) {
         nsCOMPtr<nsIDOMCSSRule> domRule = styleRule->GetDOMRule();
         if (domRule) {
-          rules->InsertElementAt(domRule, 0, /*weak =*/ false);
+          rules->AppendElement(domRule, /*weak =*/ false);
         }
       }
     }