Blink: Throttle progressively loaded images.

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 d0267f99ccf05b41ce82815333f210a8c96abad3..5f68101c75238f86cb26eff681bad68204007404 100644
--- a/third_party/WebKit/Source/core/fetch/ImageResource.cpp
+++ b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
@@ -45,6 +45,11 @@
 
 namespace blink {
 
+// The amount of time to wait before informing the clients that the image has
+// been updated (in seconds). This effectively throttles invalidations that
+// result from new data arriving for this image.
+static double flushDelaySeconds = 1.;

[pdr., 2016/10/05 02:07:31]

Should we use constexpr and a k prefix here?
E.g., "constexpr double kFlushDelaySeconds = 1.;"?

+
 ImageResource* ImageResource::fetch(FetchRequest& request,
                                     ResourceFetcher* fetcher) {
   if (request.resourceRequest().requestContext() ==
@@ -242,7 +247,18 @@ void ImageResource::appendData(const char* data, size_t length) {
     m_multipartParser->appendData(data, length);
   } else {
     Resource::appendData(data, length);
-    updateImage(false);
+
+    // If we have an animated image, then update as soon as we have more data.
+    if (m_image && m_image->maybeAnimated()) {
+      updateImage(false);
+      return;
+    }
+
+    // For other images, only update at |flushDelaySeconds| intervals.

[pdr., 2016/10/05 02:07:31]

Can you expand on this comment a bit? Similar to your comment above
flushDelaySeconds, I'd like to make it clear that we're throttling the
updateImage call to reduce invalidations.

+    double now = WTF::currentTime();
+    if (m_lastFlushTime && (m_lastFlushTime + flushDelaySeconds <= now))
+      updateImage(false);
+    m_lastFlushTime = now;
   }
 }