Fix lazyloaded image moved between document test

When an image is cleared (src='' or img element moved) lazyload state
should be reset. This allows proper lazyload handling to happen when src
is set again.

TBR=hiroshige@chromium.org

Fixed: 10019689
Change-Id: I6f5a2500d63db4e82b3400f49592e183244b12e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2164106
Commit-Queue: rajendrant <rajendrant@chromium.org>
Reviewed-by: Dominic Farolino <dom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#762633}

third_party/blink/renderer/core/loader/image_loader.cc

@@ -447,7 +447,7 @@ void ImageLoader::UpdateImageState(ImageResourceContent* new_image_content) {
     image_complete_ = true;
     if (lazy_image_load_state_ == LazyImageLoadState::kDeferred) {
       LazyImageHelper::StopMonitoring(GetElement());
-      lazy_image_load_state_ = LazyImageLoadState::kFullImage;
+      lazy_image_load_state_ = LazyImageLoadState::kNone;
     }
   } else {
     image_complete_ = false;

third_party/blink/web_tests/external/wpt/html/semantics/embedded-content/the-img-element/move-element-and-scroll-expected.txt

-This is a testharness.js-based test.
-FAIL Test that <img> below viewport is not loaded when moved to another document and then scrolled to assert_unreached: The below viewport image should not load Reached unreachable code
-Harness: the test ran to completion.
-