Fix imageSourceURL() for WebGL elements.

Source/core/html/canvas/WebGLRenderingContextBase.cpp

Index: Source/core/html/canvas/WebGLRenderingContextBase.cpp
diff --git a/Source/core/html/canvas/WebGLRenderingContextBase.cpp b/Source/core/html/canvas/WebGLRenderingContextBase.cpp
index 1159ad7039c4fcbee798f6101f5642deeb742ca0..f2ac80e6df4a8e21e51506bb63925ea883742a45 100644
--- a/Source/core/html/canvas/WebGLRenderingContextBase.cpp
+++ b/Source/core/html/canvas/WebGLRenderingContextBase.cpp
@@ -518,6 +518,7 @@ WebGLRenderingContextBase::WebGLRenderingContextBase(HTMLCanvasElement* passedCa
     , m_multisamplingObserverRegistered(false)
     , m_onePlusMaxEnabledAttribIndex(0)
     , m_onePlusMaxNonDefaultTextureUnit(0)
+    , m_savingImage(false)
 {
     ASSERT(context);
 
@@ -841,6 +842,7 @@ void WebGLRenderingContextBase::paintRenderingResultsToCanvas()
         canvas()->makePresentationCopy();
     } else
         canvas()->clearPresentationCopy();
+
     clearIfComposited();
 
     if (!m_markedCanvasDirty && !m_layerCleared)
@@ -852,7 +854,7 @@ void WebGLRenderingContextBase::paintRenderingResultsToCanvas()
     ScopedTexture2DRestorer restorer(this);
 
     m_drawingBuffer->commit();
-    if (!(canvas()->buffer())->copyRenderingResultsFromDrawingBuffer(m_drawingBuffer.get())) {
+    if (!(canvas()->buffer())->copyRenderingResultsFromDrawingBuffer(m_drawingBuffer.get(), m_savingImage)) {
         canvas()->ensureUnacceleratedImageBuffer();
         if (canvas()->hasImageBuffer())
             m_drawingBuffer->paintRenderingResultsToCanvas(canvas()->buffer());