Remove duplication of encoded image data

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

Index: third_party/WebKit/Source/core/fetch/ImageResource.cpp
diff --git a/third_party/WebKit/Source/core/fetch/ImageResource.cpp b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
index 516fed78f528dadcb49927b73ec2c0e43fcd3ecb..48347e6ed30d57939d3a5d575f2feb8aa70d518d 100644
--- a/third_party/WebKit/Source/core/fetch/ImageResource.cpp
+++ b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
@@ -124,10 +124,7 @@ void ImageResource::addObserver(ImageResourceObserver* observer)
     if (isCacheValidator())
         return;
 
-    if (m_data && !m_image && !errorOccurred()) {
-        createImage();
-        m_image->setData(m_data, true);
-    }
+    DCHECK(!m_data || m_image);
 
     if (m_image && !m_image->isNull()) {
         observer->imageChanged(this);
@@ -190,18 +187,15 @@ bool ImageResource::isSafeToUnlock() const
 
 void ImageResource::destroyDecodedDataForFailedRevalidation()
 {
-    m_image = nullptr;
-    setDecodedSize(0);
+    m_image->destroyDecodedData();

[haraken, 2016/06/23 01:26:40]

Honestly speaking, I don't fully understand changes in this file.

Would you help me understand how m_data, m_image, setDecodedSize and
destroyDecodedData are going to be handled after this CL?

[hajimehoshi, 2016/06/23 09:23:12]

Before this CL, m_data is a primary data and m_image can always be purged, but
after this CL, m_image is basically never purged and m_data is purged soon after
m_image is completed. That's why destroyDecodedDataForFailedRevalidation now
doesn't clear m_image. IIUC setDecodedSize is synched with m_image and now that
m_image is not cleared, we don't need to call setDecodedSize(0) here.

 }
 
 void ImageResource::destroyDecodedDataIfPossible()
 {
-    if (!hasClientsOrObservers() && !isLoading() && (!m_image || (m_image->hasOneRef() && m_image->isBitmapImage()))) {
-        m_image = nullptr;
-        setDecodedSize(0);
-    } else if (m_image && !errorOccurred()) {
+    if (!m_image)
+        return;
+    if ((!hasClientsOrObservers() && !isLoading() && m_image->hasOneRef() && m_image->isBitmapImage()) || !errorOccurred())
         m_image->destroyDecodedData();
-    }
 }
 
 void ImageResource::doResetAnimation()
@@ -226,6 +220,16 @@ void ImageResource::allClientsAndObserversRemoved()
     Resource::allClientsAndObserversRemoved();
 }
 
+PassRefPtr<SharedBuffer> ImageResource::resourceBuffer() const
+{
+    RefPtr<SharedBuffer> data = Resource::resourceBuffer();
+    if (data)
+        return data;
+    if (m_image)
+        return m_image->data();
+    return nullptr;
+}
+
 void ImageResource::appendData(const char* data, size_t length)
 {
     if (m_multipartParser) {
@@ -355,7 +359,6 @@ inline void ImageResource::clearImage()
     // If our Image has an observer, it's always us so we need to clear the back pointer
     // before dropping our reference.
     m_image->clearImageObserver();
-    m_image.clear();
 }
 
 void ImageResource::updateImage(bool allDataReceived)
@@ -370,7 +373,7 @@ void ImageResource::updateImage(bool allDataReceived)
     // Have the image update its data from its internal buffer.
     // It will not do anything now, but will delay decoding until
     // queried for info (like size or specific image frames).
-    if (m_image)
+    if (m_image && m_data)
         sizeAvailable = m_image->setData(m_data, allDataReceived);
 
     // Go ahead and tell our observers to try to draw if we have either
@@ -390,13 +393,15 @@ void ImageResource::updateImage(bool allDataReceived)
         // (decoding delayed until painting) that seems hard.
         notifyObservers();
     }
+
+    if (allDataReceived)
+        m_data.clear();
 }
 
 void ImageResource::updateImageAndClearBuffer()
 {
     clearImage();
     updateImage(true);
-    m_data.clear();
 }
 
 void ImageResource::finish(double loadFinishTime)