Don't load pending resources for @page descriptors.

We incorrectly parse properties like background-image as page
descriptors. This CL makes sure we at least don't trigger fetches for
such urls.

Bug: 1086264
Change-Id: I32f2262fae46cafdd57f1cf2baa825d6bef32389
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2215323Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771718}

third_party/blink/renderer/core/css/resolver/style_resolver.cc

@@ -1270,8 +1270,6 @@ scoped_refptr<const ComputedStyle> StyleResolver::StyleForPage(
         state, result.AllRules(), false, inherited_only, needs_apply_pass);
   }
 
-  state.LoadPendingResources();
-
   // Now return the style.
   return state.TakeStyle();
 }

third_party/blink/renderer/core/css/resolver/style_resolver_test.cc

@@ -326,7 +326,7 @@ const CSSImageValue& GetBackgroundImageValue(Element* element) {
 
 TEST_F(StyleResolverTest, BackgroundImageFetch) {
   GetDocument().documentElement()->setInnerHTML(R"HTML(
-    <style id="sheet">
+    <style>
       #none {
         display: none;
         background-image: url(img-none.png);
@@ -389,4 +389,28 @@ TEST_F(StyleResolverTest, BackgroundImageFetch) {
       << "No fetch for element outside the flat tree";
 }
 
+TEST_F(StyleResolverTest, NoFetchForAtPage) {
+  // Strictly, we should drop descriptors from @page rules which are not valid
+  // descriptors, but as long as we apply them to ComputedStyle we should at
+  // least not trigger fetches. The display:contents is here to make sure we
+  // don't hit a DCHECK in StylePendingImage::ComputedCSSValue().
+  GetDocument().body()->setInnerHTML(R"HTML(
+    <style>
+      @page {
+        display: contents;
+        background-image: url(bg-img.png);
+      }
+    </style>
+  )HTML");
+
+  scoped_refptr<const ComputedStyle> page_style =
+      GetDocument().EnsureStyleResolver().StyleForPage(0, "");
+  ASSERT_TRUE(page_style);
+  const CSSValue* computed_value = ComputedStyleUtils::ComputedPropertyValue(
+      GetCSSPropertyBackgroundImage(), *page_style);
+
+  const CSSValueList* bg_img_list = To<CSSValueList>(computed_value);
+  EXPECT_TRUE(To<CSSImageValue>(bg_img_list->Item(0)).IsCachePending());
+}
+
 }  // namespace blink