Avoid calling selectImageSource when attribute value didn't change

https://bugs.webkit.org/show_bug.cgi?id=267315

Reviewed by Alex Christensen.

This PR adds a fast path for setting src to the same value in HTMLImageElement::attributeChanged.
In this case, we check whether image loading is observable or not (e.g. has a service worker),
and it if isn't, we avoid going through the full image loading path and simply fire the load event instead.

* Source/WebCore/html/HTMLImageElement.cpp:
(WebCore::HTMLImageElement::attributeChanged):
* Source/WebCore/loader/ImageLoader.cpp:
(WebCore::ImageLoader::updateFromElementIgnoringPreviousErrorToSameValue):
* Source/WebCore/loader/ImageLoader.h:

Canonical link: https://commits.webkit.org/273148@main

Source/WebCore/html/HTMLImageElement.cpp

@@ -356,7 +356,10 @@ void HTMLImageElement::attributeChanged(const QualifiedName& name, const AtomStr
     case AttributeNames::srcAttr:
     case AttributeNames::srcsetAttr:
     case AttributeNames::sizesAttr:
-        selectImageSource(RelevantMutation::Yes);
+        if (oldValue != newValue)
+            selectImageSource(RelevantMutation::Yes);
+        else
+            m_imageLoader->updateFromElementIgnoringPreviousErrorToSameValue();
         break;
     case AttributeNames::usemapAttr:
         if (isInTreeScope() && !m_parsedUsemap.isNull())

Source/WebCore/loader/ImageLoader.cpp

@@ -339,6 +339,19 @@ void ImageLoader::updateFromElementIgnoringPreviousError(RelevantMutation releva
     updateFromElement(relevantMutation);
 }
 
+void ImageLoader::updateFromElementIgnoringPreviousErrorToSameValue()
+{
+    if ((m_image && !m_image->allowsCaching()) || !m_failedLoadURL.isEmpty() || element().document().activeServiceWorker()) {
+        updateFromElementIgnoringPreviousError(RelevantMutation::Yes);
+        return;
+    }
+    if (m_hasPendingLoadEvent || !m_pendingURL.isEmpty())
+        return;
+    ASSERT(m_image);
+    m_hasPendingLoadEvent = true;
+    notifyFinished(*m_image, NetworkLoadMetrics { });
+}
+
 static inline void resolvePromises(Vector<RefPtr<DeferredPromise>>& promises)
 {
     ASSERT(!promises.isEmpty());

Source/WebCore/loader/ImageLoader.h

@@ -53,10 +53,12 @@ class ImageLoader : public CachedImageClient {
     // loading if a load hasn't already been started.
     void updateFromElement(RelevantMutation = RelevantMutation::No);
 
-    // This function should be called whenever the 'src' attribute is set, even if its value
-    // doesn't change; starts new load unconditionally (matches Firefox and Opera behavior).
+    // This function should be called whenever the 'src' attribute is set.
+    // Starts new load unconditionally (matches Firefox and Opera behavior).
     void updateFromElementIgnoringPreviousError(RelevantMutation = RelevantMutation::No);
 
+    void updateFromElementIgnoringPreviousErrorToSameValue();
+
     void elementDidMoveToNewDocument(Document&);
 
     Element& element() { return m_element; }