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

Source/core/platform/graphics/ImageSource.cpp

Index: Source/core/platform/graphics/ImageSource.cpp
diff --git a/Source/core/platform/graphics/ImageSource.cpp b/Source/core/platform/graphics/ImageSource.cpp
index c6395a09f0828fd316edda4dbe8f22a2e9d57c88..4a43d3c685f3d648a7d03c64f24a8af8a90be33a 100644
--- a/Source/core/platform/graphics/ImageSource.cpp
+++ b/Source/core/platform/graphics/ImageSource.cpp
@@ -156,20 +156,16 @@ PassNativeImagePtr ImageSource::createFrameAtIndex(size_t index)
     return buffer->asNewNativeImage();
 }
 
-float ImageSource::frameDurationAtIndex(size_t index)
+float ImageSource::frameDurationAtIndex(size_t index) const
 {
     if (!m_decoder)
         return 0;
 
-    ImageFrame* buffer = m_decoder->frameBufferAtIndex(index);
-    if (!buffer || buffer->status() == ImageFrame::FrameEmpty)
-        return 0;
-
     // Many annoying ads specify a 0 duration to make an image flash as quickly as possible.
     // We follow Firefox's behavior and use a duration of 100 ms for any frames that specify
     // a duration of <= 10 ms. See <rdar://problem/7689300> and <http://webkit.org/b/36082>
     // for more information.
-    const float duration = buffer->duration() / 1000.0f;
+    const float duration = m_decoder->frameDurationAtIndex(index) / 1000.0f;
     if (duration < 0.011f)
         return 0.100f;
     return duration;
@@ -180,20 +176,14 @@ ImageOrientation ImageSource::orientationAtIndex(size_t) const
     return m_decoder ? m_decoder->orientation() : DefaultImageOrientation;
 }
 
-bool ImageSource::frameHasAlphaAtIndex(size_t index)
+bool ImageSource::frameHasAlphaAtIndex(size_t index) const
 {
-    if (!m_decoder)
-        return true;
-    return m_decoder->frameHasAlphaAtIndex(index);
+    return !m_decoder || m_decoder->frameHasAlphaAtIndex(index);
 }
 
-bool ImageSource::frameIsCompleteAtIndex(size_t index)
+bool ImageSource::frameIsCompleteAtIndex(size_t index) const
 {
-    if (!m_decoder)
-        return false;
-
-    ImageFrame* buffer = m_decoder->frameBufferAtIndex(index);
-    return buffer && buffer->status() == ImageFrame::FrameComplete;
+    return m_decoder && m_decoder->frameIsCompleteAtIndex(index);
 }
 
 unsigned ImageSource::frameBytesAtIndex(size_t index) const