The position of opaque black rect is incorrect when alpha is false.

Source/core/html/HTMLCanvasElement.cpp

Index: Source/core/html/HTMLCanvasElement.cpp
diff --git a/Source/core/html/HTMLCanvasElement.cpp b/Source/core/html/HTMLCanvasElement.cpp
index 5780844c5bb9ea8df58e85c1974398f2bbe6a2e1..24e3d37f9a7633739c322c328f8b529cccc0d10e 100644
--- a/Source/core/html/HTMLCanvasElement.cpp
+++ b/Source/core/html/HTMLCanvasElement.cpp
@@ -322,7 +322,7 @@ void HTMLCanvasElement::paint(GraphicsContext* context, const LayoutRect& r)
     } else {
         // When alpha is false, we should draw to opaque black.
         if (m_context && !m_context->hasAlpha())
-            context->fillRect(FloatRect(0, 0, width(), height()), Color(0, 0, 0));
+            context->fillRect(FloatRect(r), Color(0, 0, 0));
     }
 
     if (is3D())