webgl/canvas: Missing null check for PaintImage.

R=zmo@chromium.org

Bug: 974485,976060
Change-Id: Ifd40d06facc31e0f9e0629490cb1a136c0fad0c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663736
Auto-Submit: Khushal <khushalsagar@chromium.org>
Commit-Queue: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670250}

third_party/blink/renderer/modules/webgl/webgl_rendering_context_base.cc

@@ -1644,7 +1644,7 @@ bool WebGLRenderingContextBase::CopyRenderingResultsFromDrawingBuffer(
   // is a separate path for the accelerated case is that we assume texture
   // copying is faster than drawImage.
   scoped_refptr<StaticBitmapImage> image = GetImage(kPreferAcceleration);
-  if (!image)
+  if (!image || !image->PaintImageForCurrentFrame())
     return false;
   cc::PaintFlags paint_flags;
   paint_flags.setBlendMode(SkBlendMode::kSrc);