safety checks to prevent dereferencing null

content/base/src/nsStyleSet.cpp

@@ -533,7 +533,10 @@ nsIStyleContext* StyleSetImpl::ResolveStyleFor(nsIPresContext* aPresContext,
 
     if (nsnull != rules) {
       nsIAtom* medium = nsnull;
-      aPresContext->GetMedium(&medium);
+      NS_ASSERTION(aPresContext, "must have aPresContext");
+      if (aPresContext) {
+	      aPresContext->GetMedium(&medium);
+      }
       RulesMatchingData data(aPresContext, medium, aContent, aParentContext, rules);
       if (mBackstopSheets) {
         mBackstopSheets->EnumerateBackwards(EnumRulesMatching, &data);

content/html/style/src/nsCSSStyleSheet.cpp

@@ -1644,7 +1644,10 @@ PRInt32 CSSStyleSheetImpl::RulesMatching(nsIPresContext* aPresContext,
 
   PRInt32 matchCount = 0;
 
+  if (!aPresContext || !aContent || !aResults) return matchCount;
+
   nsIAtom* presMedium = nsnull;
+
   aPresContext->GetMedium(&presMedium);
 
   RuleCascadeData* cascade = GetRuleCascade(presMedium);

content/html/style/src/nsHTMLCSSStyleSheet.cpp

@@ -425,6 +425,8 @@ PRInt32 HTMLCSSStyleSheetImpl::RulesMatching(nsIPresContext* aPresContext,
 
   PRInt32 matchCount = 0;
 
+  if (!aPresContext || !aContent || !aResults) return matchCount;
+
   nsIStyledContent* styledContent;
 
   // just get the one and only style rule from the content's STYLE attribute

content/html/style/src/nsHTMLStyleSheet.cpp

@@ -553,6 +553,8 @@ PRInt32 HTMLStyleSheetImpl::RulesMatching(nsIPresContext* aPresContext,
 
   PRInt32 matchCount = 0;
 
+  if (!aPresContext || !aContent || !aResults) return matchCount;
+
   nsIStyledContent* styledContent;
   if (NS_SUCCEEDED(aContent->QueryInterface(nsIStyledContent::GetIID(), (void**)&styledContent))) {
     PRInt32 nameSpace;

layout/base/src/nsStyleSet.cpp

@@ -533,7 +533,10 @@ nsIStyleContext* StyleSetImpl::ResolveStyleFor(nsIPresContext* aPresContext,
 
     if (nsnull != rules) {
       nsIAtom* medium = nsnull;
-      aPresContext->GetMedium(&medium);
+      NS_ASSERTION(aPresContext, "must have aPresContext");
+      if (aPresContext) {
+	      aPresContext->GetMedium(&medium);
+      }
       RulesMatchingData data(aPresContext, medium, aContent, aParentContext, rules);
       if (mBackstopSheets) {
         mBackstopSheets->EnumerateBackwards(EnumRulesMatching, &data);

layout/html/style/src/nsCSSStyleSheet.cpp

@@ -1644,7 +1644,10 @@ PRInt32 CSSStyleSheetImpl::RulesMatching(nsIPresContext* aPresContext,
 
   PRInt32 matchCount = 0;
 
+  if (!aPresContext || !aContent || !aResults) return matchCount;
+
   nsIAtom* presMedium = nsnull;
+
   aPresContext->GetMedium(&presMedium);
 
   RuleCascadeData* cascade = GetRuleCascade(presMedium);

layout/html/style/src/nsHTMLCSSStyleSheet.cpp

@@ -425,6 +425,8 @@ PRInt32 HTMLCSSStyleSheetImpl::RulesMatching(nsIPresContext* aPresContext,
 
   PRInt32 matchCount = 0;
 
+  if (!aPresContext || !aContent || !aResults) return matchCount;
+
   nsIStyledContent* styledContent;
 
   // just get the one and only style rule from the content's STYLE attribute

layout/html/style/src/nsHTMLStyleSheet.cpp

@@ -553,6 +553,8 @@ PRInt32 HTMLStyleSheetImpl::RulesMatching(nsIPresContext* aPresContext,
 
   PRInt32 matchCount = 0;
 
+  if (!aPresContext || !aContent || !aResults) return matchCount;
+
   nsIStyledContent* styledContent;
   if (NS_SUCCEEDED(aContent->QueryInterface(nsIStyledContent::GetIID(), (void**)&styledContent))) {
     PRInt32 nameSpace;

layout/style/nsCSSStyleSheet.cpp

@@ -1644,7 +1644,10 @@ PRInt32 CSSStyleSheetImpl::RulesMatching(nsIPresContext* aPresContext,
 
   PRInt32 matchCount = 0;
 
+  if (!aPresContext || !aContent || !aResults) return matchCount;
+
   nsIAtom* presMedium = nsnull;
+
   aPresContext->GetMedium(&presMedium);
 
   RuleCascadeData* cascade = GetRuleCascade(presMedium);

layout/style/nsHTMLCSSStyleSheet.cpp

@@ -425,6 +425,8 @@ PRInt32 HTMLCSSStyleSheetImpl::RulesMatching(nsIPresContext* aPresContext,
 
   PRInt32 matchCount = 0;
 
+  if (!aPresContext || !aContent || !aResults) return matchCount;
+
   nsIStyledContent* styledContent;
 
   // just get the one and only style rule from the content's STYLE attribute

layout/style/nsHTMLStyleSheet.cpp

@@ -553,6 +553,8 @@ PRInt32 HTMLStyleSheetImpl::RulesMatching(nsIPresContext* aPresContext,
 
   PRInt32 matchCount = 0;
 
+  if (!aPresContext || !aContent || !aResults) return matchCount;
+
   nsIStyledContent* styledContent;
   if (NS_SUCCEEDED(aContent->QueryInterface(nsIStyledContent::GetIID(), (void**)&styledContent))) {
     PRInt32 nameSpace;

layout/style/nsStyleSet.cpp

@@ -533,7 +533,10 @@ nsIStyleContext* StyleSetImpl::ResolveStyleFor(nsIPresContext* aPresContext,
 
     if (nsnull != rules) {
       nsIAtom* medium = nsnull;
-      aPresContext->GetMedium(&medium);
+      NS_ASSERTION(aPresContext, "must have aPresContext");
+      if (aPresContext) {
+	      aPresContext->GetMedium(&medium);
+      }
       RulesMatchingData data(aPresContext, medium, aContent, aParentContext, rules);
       if (mBackstopSheets) {
         mBackstopSheets->EnumerateBackwards(EnumRulesMatching, &data);