CSSStyleSheetResource should cache decoded text instead of raw bytes

third_party/WebKit/Source/core/fetch/CSSStyleSheetResource.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 74 matching lines @@
         static_cast<StyleSheetResourceClient*>(c)->didAppendFirstData(this);
 
     // |c| might be removed in didAppendFirstData, so ensure it is still a
     // client.
     if (hasClient(c) && !isLoading())
         static_cast<StyleSheetResourceClient*>(c)->setCSSStyleSheet(resourceRequest().url(), response().url(), encoding(), this);
 }
 
 const String CSSStyleSheetResource::sheetText(MIMETypeCheck mimeTypeCheck) const
 {
-    if (!data() || data()->isEmpty() || !canUseSheet(mimeTypeCheck))
+    if (!canUseSheet(mimeTypeCheck))
         return String();
 
-    if (!m_decodedSheetText.isNull())
+    // Use cached decoded sheet text when available
+    if (!m_decodedSheetText.isNull()) {
+        // We should have the decoded sheet text cached when the resource is fully loaded.
+        DCHECK(getStatus() != Resource::Cached);
+
         return m_decodedSheetText;
+    }
 
-    // Don't cache the decoded text, regenerating is cheap and it can use quite a bit of memory
+    if (!data() || data()->isEmpty())
+        return String();
+
     return decodedText();
 }
 
 void CSSStyleSheetResource::appendData(const char* data, size_t length)
 {
     Resource::appendData(data, length);
     if (m_didNotifyFirstData)
         return;
     ResourceClientWalker<StyleSheetResourceClient> w(clients());
     while (StyleSheetResourceClient* c = w.next())
         c->didAppendFirstData(this);
     m_didNotifyFirstData = true;
 }
 
 void CSSStyleSheetResource::checkNotify()
 {
-    // Decode the data to find out the encoding and keep the sheet text around during checkNotify()
-    if (data())
+    // Decode the data to find out the encoding and cache the decoded sheet text.
+    if (data()) {
         m_decodedSheetText = decodedText();
+        clearData();
+    }
 
     ResourceClientWalker<StyleSheetResourceClient> w(clients());
     while (StyleSheetResourceClient* c = w.next())
         c->setCSSStyleSheet(resourceRequest().url(), response().url(), encoding(), this);
-    // Clear the decoded text as it is unlikely to be needed immediately again and is cheap to regenerate.
-    m_decodedSheetText = String();
 }
 
 void CSSStyleSheetResource::destroyDecodedDataIfPossible()
 {
+    m_decodedSheetText = String();

[hiroshige, 2016/08/31 10:34:53]

Probably clearing |m_decodedSheetText| in destroyDecodedDataIfPossible() will
cause an error when prune() is called: after |m_decodedSheetText| is cleared,
the CSSStyleSheetResource is no longer reusable. Waiting for bot results.

     if (!m_parsedStyleSheetCache)
         return;
 
     setParsedStyleSheetCache(nullptr);
     setDecodedSize(0);
 }
 
 bool CSSStyleSheetResource::canUseSheet(MIMETypeCheck mimeTypeCheck) const
 {
     if (errorOccurred())
@@ skipping 41 matching lines @@
         // This stylesheet resource did conflict with another resource and was
         // not added to the cache.
         setParsedStyleSheetCache(nullptr);
         return;
     }
     setParsedStyleSheetCache(sheet);
     setDecodedSize(m_parsedStyleSheetCache->estimatedSizeInBytes());
 }
 
 } // namespace blink