Fix crash in CSSStyleSheetResource::appendData

third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp

Index: third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
diff --git a/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp b/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
index 19e8b68357cf27bd712ecd7bb63d734d2f68796a..6be45f8e9fd1e327855f9edae52571d88d84fa12 100644
--- a/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
+++ b/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
@@ -242,10 +242,22 @@ CSSPreloaderResourceClient::CSSPreloaderResourceClient(Resource* resource, HTMLR
 {
 }
 
+void CSSPreloaderResourceClient::stopObserving()
+{
+    if (m_resource) {
+        m_resource->removeClient(this);
+        m_resource.clear();
+    }
+}
+
+CSSPreloaderResourceClient::~CSSPreloaderResourceClient()
+{
+    stopObserving();

[Nate Chapin, 2016/05/03 18:25:30]

Alternately, you can have CSSPreloaderResourceClient inherit
ResourceOwner<CSSStyleSheetResource>.

[Charlie Harrison, 2016/05/03 20:32:11]

Very good point. Thanks for the suggestion.

+}
+
 void CSSPreloaderResourceClient::notifyFinished(Resource* resource)
 {
-    resource->removeClient(this);
-    m_resource.clear();
+    stopObserving();
 }
 
 // Only attach for one appendData call, as that's where most imports will likely
@@ -267,8 +279,7 @@ void CSSPreloaderResourceClient::didAppendFirstData(const CSSStyleSheetResource*
         DEFINE_STATIC_LOCAL(CustomCountHistogram, cssImportHistogram, ("PreloadScanner.ExternalCSS.PreloadCount", 1, 100, 50));
         cssImportHistogram.count(m_preloader->countPreloads() - currentPreloadCount);
     }
-    m_resource->removeClient(this);
-    m_resource.clear();
+    stopObserving();
 }
 
 } // namespace blink