blink/canvas: Fix incorrect lifetime assumptions for context loss.

After the change in [1], we no longer ensure that the SkCanvas lifetime
is tied to CanvasImageProvider.

[1] : https://chromium-review.googlesource.com/c/chromium/src/+/2450842

R=aaronhk@chromium.org

Bug: 1143229
Change-Id: If99ff121c221b6560da58596fc9faf11fe28dfeb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2528615
Auto-Submit: Khushal <khushalsagar@chromium.org>
Commit-Queue: Juanmi Huertas <juanmihd@chromium.org>
Reviewed-by: Juanmi Huertas <juanmihd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825815}

third_party/blink/renderer/platform/graphics/canvas_resource_provider.cc

@@ -1155,14 +1155,9 @@ cc::PaintCanvas* CanvasResourceProvider::Canvas() {
 }
 
 void CanvasResourceProvider::OnContextDestroyed() {
-  if (canvas_image_provider_) {
-    if (!UseOopRasterization()) {
-      DCHECK(skia_canvas_);
-      skia_canvas_->reset_image_provider();
-    }
-
-    canvas_image_provider_.reset();
-  }
+  if (skia_canvas_)
+    skia_canvas_->reset_image_provider();
+  canvas_image_provider_.reset();
 }
 
 void CanvasResourceProvider::OnFlushForImage(PaintImage::ContentId content_id) {