Checking if frame is complete and access duration doesn't need a decode

Source/core/platform/image-decoders/ImageDecoder.cpp

Index: Source/core/platform/image-decoders/ImageDecoder.cpp
diff --git a/Source/core/platform/image-decoders/ImageDecoder.cpp b/Source/core/platform/image-decoders/ImageDecoder.cpp
index 7bbf39fc271f210770ecfcc5e73ea16ca6ba1907..884542a1ab79fcc0afece4bbe1df2786c6afc74c 100644
--- a/Source/core/platform/image-decoders/ImageDecoder.cpp
+++ b/Source/core/platform/image-decoders/ImageDecoder.cpp
@@ -120,11 +120,13 @@ PassOwnPtr<ImageDecoder> ImageDecoder::create(const SharedBuffer& data, ImageSou
 
 bool ImageDecoder::frameHasAlphaAtIndex(size_t index) const
 {
-    if (m_frameBufferCache.size() <= index)
-        return true;
-    if (m_frameBufferCache[index].status() == ImageFrame::FrameComplete)
-        return m_frameBufferCache[index].hasAlpha();
-    return true;
+    return !frameIsCompleteAtIndex(index) || m_frameBufferCache[index].hasAlpha();
+}
+
+bool ImageDecoder::frameIsCompleteAtIndex(size_t index) const
+{
+    return (index < m_frameBufferCache.size()) &&
+        (m_frameBufferCache[index].status() == ImageFrame::FrameComplete);
 }
 
 unsigned ImageDecoder::frameBytesAtIndex(size_t index) const