Error event shouldn't fire when image is updated on environment changes.

Source/core/loader/ImageLoader.cpp

Index: Source/core/loader/ImageLoader.cpp
diff --git a/Source/core/loader/ImageLoader.cpp b/Source/core/loader/ImageLoader.cpp
index c89b49fc21096ea00e9107972d5d4a97d6f7eba7..cbf21345934a8b820f37918559a9a6d88ce9040e 100644
--- a/Source/core/loader/ImageLoader.cpp
+++ b/Source/core/loader/ImageLoader.cpp
@@ -120,6 +120,7 @@ ImageLoader::ImageLoader(Element* element)
     , m_imageComplete(true)
     , m_loadingImageDocument(false)
     , m_elementIsProtected(false)
+    , m_environmentChangeOnly(false)
     , m_highPriorityClientCount(0)
 {
     WTF_LOG(Timers, "new ImageLoader %p", this);
@@ -308,6 +309,9 @@ void ImageLoader::doUpdateFromElement(BypassMainWorldBehavior bypassBehavior, Up
         toRenderImage(m_element->renderer())->intrinsicSizeChanged();
     }
 
+    if (updateBehavior == UpdateSizeChanged)
+        m_environmentChangeOnly = true;

[Mike West, 2014/10/17 14:12:40]

You can drop the `if` and just assign the result of the comparison to the
variable.

+
     if (RenderImageResource* imageResource = renderImageResource())
         imageResource->resetAnimation();
 
@@ -318,6 +322,7 @@ void ImageLoader::doUpdateFromElement(BypassMainWorldBehavior bypassBehavior, Up
 
 void ImageLoader::updateFromElement(UpdateFromElementBehavior updateBehavior, LoadType loadType)
 {
+    m_environmentChangeOnly = false;
     AtomicString imageSourceURL = m_element->imageSourceURL();
 
     if (updateBehavior == UpdateIgnorePreviousError)
@@ -386,8 +391,12 @@ void ImageLoader::notifyFinished(Resource* resource)
         loadEventSender().cancelEvent(this);
         m_hasPendingLoadEvent = false;
 
-        m_hasPendingErrorEvent = true;
-        errorEventSender().dispatchEventSoon(this);
+        // The error event should not fire if the image data update is a result of environment change.
+        // https://html.spec.whatwg.org/multipage/embedded-content.html#the-img-element:the-img-element-55
+        if (!m_environmentChangeOnly) {
+            m_hasPendingErrorEvent = true;
+            errorEventSender().dispatchEventSoon(this);
+        }
 
         // Only consider updating the protection ref-count of the Element immediately before returning
         // from this function as doing so might result in the destruction of this ImageLoader.