canvas: make a temporary buffer when a context doesn't exist.

Source/core/imagebitmap/ImageBitmapFactories.cpp

Index: Source/core/imagebitmap/ImageBitmapFactories.cpp
diff --git a/Source/core/imagebitmap/ImageBitmapFactories.cpp b/Source/core/imagebitmap/ImageBitmapFactories.cpp
index ac39e7032e001e5c89048930235a59cff6d70ac8..25ae75c32f85d3a072a9204c0aab77d9fe66667b 100644
--- a/Source/core/imagebitmap/ImageBitmapFactories.cpp
+++ b/Source/core/imagebitmap/ImageBitmapFactories.cpp
@@ -178,7 +178,7 @@ ScriptPromise ImageBitmapFactories::createImageBitmap(ScriptState* scriptState,
     }
 
     // FIXME: make ImageBitmap creation asynchronous crbug.com/258082
-    return fulfillImageBitmap(scriptState, canvas->buffer() ? ImageBitmap::create(canvas, IntRect(sx, sy, sw, sh)) : nullptr);
+    return fulfillImageBitmap(scriptState, canvas->isDrawable() ? ImageBitmap::create(canvas, IntRect(sx, sy, sw, sh)) : nullptr);
 }
 
 ScriptPromise ImageBitmapFactories::createImageBitmap(ScriptState* scriptState, EventTarget& eventTarget, Blob* blob, ExceptionState& exceptionState)