ImageContextImpl: fix a wrong DCHECK in CreateFallbackImage()

Bug: 974359
Change-Id: Idcc3c80eda39d4c94470c7f5542fea68dc65cc0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1751823
Commit-Queue: Peng Huang <penghuang@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Auto-Submit: Peng Huang <penghuang@chromium.org>
Reviewed-by: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686434}

components/viz/service/display_embedder/image_context_impl.cc

@@ -44,7 +44,7 @@ ImageContextImpl::~ImageContextImpl() {
 
 void ImageContextImpl::CreateFallbackImage(
     gpu::SharedContextState* context_state) {
-  DCHECK(!context_state);
+  DCHECK(!fallback_context_state_);
   fallback_context_state_ = context_state;
 
   SkColorType color_type = ResourceFormatToClosestSkColorType(