Speculative fix for crash in Canvas2DLayerBridge

BUG=759412

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Id742ca0ffae8e2e1aa55e8b324478c09189bbaf0
Reviewed-on: https://chromium-review.googlesource.com/744503Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Commit-Queue: Justin Novosad <junov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512839}

third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp

@@ -418,6 +418,11 @@ bool Canvas2DLayerBridge::PrepareMailboxFromImage(
 
   sk_sp<SkImage> skia_image = image->PaintImageForCurrentFrame().GetSkImage();
 
+  // This check should not be necessary, it is a speculative fix for
+  // crbug.com/759412
+  if (!skia_image || !skia_image->getTexture())
+    return false;
+
   if (RuntimeEnabledFeatures::Canvas2dImageChromiumEnabled()) {
     if (PrepareGpuMemoryBufferMailboxFromImage(skia_image.get(), mailbox_info,
                                                out_mailbox))
@@ -975,6 +980,7 @@ bool Canvas2DLayerBridge::PrepareTextureMailbox(
 
   {
     sk_sp<SkImage> skImage = image->PaintImageForCurrentFrame().GetSkImage();
+    DCHECK(skImage->isTextureBacked());
     // Early exit if canvas was not drawn to since last prepareMailbox.
     GLenum filter = GetGLFilter();
     if (skImage->uniqueID() == last_image_id_ && filter == last_filter_)