Raise the loading priority of in-viewport images.

Source/core/fetch/ResourceLoadPriorityOptimizer.cpp

Index: Source/core/fetch/ResourceLoadPriorityOptimizer.cpp
diff --git a/Source/core/fetch/ResourceLoadPriorityOptimizer.cpp b/Source/core/fetch/ResourceLoadPriorityOptimizer.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..2282b836a47ef025eeb58cfee26ca68ede0d3dc6
--- /dev/null
+++ b/Source/core/fetch/ResourceLoadPriorityOptimizer.cpp
@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2013 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "core/fetch/ResourceLoadPriorityOptimizer.h"
+
+namespace WebCore {
+
+ResourceLoadPriorityOptimizer::ResourceAndVisibility::ResourceAndVisibility(ImageResource* img, VisibilityStatus v)
+    : imageResource(img)
+    , status(v)
+{
+}
+
+ResourceLoadPriorityOptimizer::ResourceAndVisibility::ResourceAndVisibility()
+    : imageResource(0)
+    , status(NotVisible)
+{
+}
+
+ResourceLoadPriorityOptimizer::ResourceAndVisibility::~ResourceAndVisibility()
+{
+}
+
+ResourceLoadPriorityOptimizer::ResourceLoadPriorityOptimizer()
+{
+}
+
+ResourceLoadPriorityOptimizer::~ResourceLoadPriorityOptimizer()
+{
+    updateImageResourcesWithLoadPriority();
+}
+
+void ResourceLoadPriorityOptimizer::updateImageResourcesWithLoadPriority()
+{
+    for (ImageResourceMap::iterator it = m_imageResources.begin(); it != m_imageResources.end(); ++it) {
+        ResourceLoadPriority priority = it->value.status == Visible ?
+            ResourceLoadPriorityLow : ResourceLoadPriorityVeryLow;
+
+        if (priority != it->value.imageResource->resourceRequest().priority()) {
+            it->value.imageResource->resourceRequest().setPriority(priority);
+            it->value.imageResource->didChangePriority(priority);
+        }
+    }
+    m_imageResources.clear();
+}
+
+void ResourceLoadPriorityOptimizer::notifyImageResourceVisibility(ImageResource* img, VisibilityStatus status)

[abarth-chromium, 2013/12/02 19:34:56]

img -> image

(Please use complete words in variable names)

[shatch, 2013/12/02 22:32:46]

Done.

+{
+    if (!img || img->isLoaded())

[eseidel, 2013/11/27 20:58:35]

Yes!  Sorry, missed this in my first pass.

+        return;
+
+    if (status == Visible) {
+        m_imageResources.set(img->identifier(), ResourceAndVisibility(img, status));
+    } else {
+        // If the resource exists in the map, don't overwrite since it might have been visible from

[eseidel, 2013/11/27 20:58:35]

Shouldn't we just always call add?  I guess you want to override in the case
where it is in the map as invisible but now we think it's visible, but not the
other way.

AddResult result = m_imageResources.add(...);
// If we already had an entry and it wasn't visible, make sure to mark it as now
visible.
if (!addResult.wasNew && status == Visible) {
   addResult.value.status = Visible;
}

I doubt it really matters either way. The two lines differing only by "add" vs.
"set" confused me at first.

[shatch, 2013/12/02 22:32:46]

Reworked it a little bit to be less confusing.

+        // some other RenderObject. HashMap::add will only add the value if the key doesn't exist in
+        // the table.
+        m_imageResources.add(img->identifier(), ResourceAndVisibility(img, status));
+    }
+}
+
+}