CSSStyleSheetResource should cache decoded text instead of raw bytes

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

Index: third_party/WebKit/Source/core/fetch/CSSStyleSheetResource.cpp
diff --git a/third_party/WebKit/Source/core/fetch/CSSStyleSheetResource.cpp b/third_party/WebKit/Source/core/fetch/CSSStyleSheetResource.cpp
index f44d16a3fcff570c6df1692629a9cc5dde000860..614bc48e55ed0e82bb4938648155bd6d25177184 100644
--- a/third_party/WebKit/Source/core/fetch/CSSStyleSheetResource.cpp
+++ b/third_party/WebKit/Source/core/fetch/CSSStyleSheetResource.cpp
@@ -92,13 +92,20 @@ void CSSStyleSheetResource::didAddClient(ResourceClient* c)
 
 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;
+    }
+
+    if (!data() || data()->isEmpty())
+        return String();
 
-    // Don't cache the decoded text, regenerating is cheap and it can use quite a bit of memory
     return decodedText();
 }
 
@@ -115,19 +122,20 @@ void CSSStyleSheetResource::appendData(const char* data, size_t length)
 
 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;