Fix crash due to null frame() pointer on Document.

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 529eeacdac90fc96732b1c022f1d980609b5b983..aff39ecf68c5a14be6c5f36e8f1f5e13b77defe7 100644
--- a/Source/core/html/HTMLCanvasElement.cpp
+++ b/Source/core/html/HTMLCanvasElement.cpp
@@ -437,7 +437,7 @@ bool HTMLCanvasElement::shouldAccelerate(const IntSize& size) const
 
     // Do not use acceleration for small canvases, unless GPU rasterization is available.
     // GPU raterization is a heuristic to avoid difficult content & whitelist targeted content.
-    if (!document().frame()->chromeClient().usesGpuRasterization() && size.width() * size.height() < settings->minimumAccelerated2dCanvasSize())
+    if (!(document().frame() && document().frame()->chromeClient().usesGpuRasterization()) && size.width() * size.height() < settings->minimumAccelerated2dCanvasSize())
         return false;
 
     if (!blink::Platform::current()->canAccelerate2dCanvas())