Web Animations API: Sort keyframes by offset

Source/core/animation/EffectInput.cpp

Index: Source/core/animation/EffectInput.cpp
diff --git a/Source/core/animation/EffectInput.cpp b/Source/core/animation/EffectInput.cpp
index 8e29bd8af94b7cc39935f1424c521f9e612da42e..cc881448986035aa7f9fc34b33d2a95868fcb00f 100644
--- a/Source/core/animation/EffectInput.cpp
+++ b/Source/core/animation/EffectInput.cpp
@@ -38,6 +38,7 @@
 #include "core/css/parser/BisonCSSParser.h"
 #include "core/css/resolver/StyleResolver.h"
 #include "core/dom/Element.h"
+#include "wtf/NonCopyingSort.h"
 
 namespace WebCore {
 
@@ -59,14 +60,23 @@ PassRefPtrWillBeRawPtr<AnimationEffect> EffectInput::convert(Element* element, c
 
     StyleSheetContents* styleSheetContents = element->document().elementSheet().contents();
     StringKeyframeVector keyframes;
+    bool everyFrameHasOffset = true;
+    bool looselySortedByOffset = true;
+    double lastOffset = -std::numeric_limits<double>::infinity();
 
     for (size_t i = 0; i < keyframeDictionaryVector.size(); ++i) {
         RefPtrWillBeRawPtr<StringKeyframe> keyframe = StringKeyframe::create();
         keyframes.append(keyframe);
 
         double offset;
-        if (keyframeDictionaryVector[i].get("offset", offset))
+        if (keyframeDictionaryVector[i].get("offset", offset)) {
             keyframe->setOffset(offset);
+            if (offset < lastOffset)
+                looselySortedByOffset = false;
+            lastOffset = offset;
+        } else {
+            everyFrameHasOffset = false;
+        }
 
         String compositeString;
         keyframeDictionaryVector[i].get("composite", compositeString);
@@ -93,6 +103,14 @@ PassRefPtrWillBeRawPtr<AnimationEffect> EffectInput::convert(Element* element, c
         }
     }
 
+    if (!looselySortedByOffset) {
+        if (!everyFrameHasOffset) {
+            exceptionState.throwDOMException(InvalidModificationError, "Keyframes are not loosely sorted by offset.");
+            return nullptr;
+        }
+        nonCopyingSort(keyframes.begin(), keyframes.end(), Keyframe::compareOffsets);
+    }
+
     RefPtrWillBeRawPtr<StringKeyframeEffectModel> keyframeEffectModel = StringKeyframeEffectModel::create(keyframes);
     if (!keyframeEffectModel->isReplaceOnly()) {
         exceptionState.throwDOMException(NotSupportedError, "Partial keyframes are not supported.");