Fix crash in LayoutObject::FirstLineStyleWithoutFallback()

Bug: 1025907
Change-Id: I7849f4decfd800f1608a231c1ae038b4ec56e90f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2136882Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757097}

third_party/blink/renderer/core/layout/layout_object.cc

@@ -3540,9 +3540,12 @@ const ComputedStyle* LayoutObject::FirstLineStyleWithoutFallback() const {
       // it's based on first_line_block's style. We need to get the uncached
       // first line style based on this object's style and cache the result in
       // it.
-      return StyleRef().AddCachedPseudoElementStyle(
-          first_line_block->GetUncachedPseudoElementStyle(
-              PseudoElementStyleRequest(kPseudoIdFirstLine), Style()));
+      if (scoped_refptr<ComputedStyle> first_line_style =
+              first_line_block->GetUncachedPseudoElementStyle(
+                  PseudoElementStyleRequest(kPseudoIdFirstLine), Style())) {
+        return StyleRef().AddCachedPseudoElementStyle(
+            std::move(first_line_style));
+      }
     }
   } else if (!IsAnonymous() && IsLayoutInline() &&
              !GetNode()->IsFirstLetterPseudoElement()) {
@@ -3554,9 +3557,12 @@ const ComputedStyle* LayoutObject::FirstLineStyleWithoutFallback() const {
             Parent()->FirstLineStyleWithoutFallback()) {
       // A first-line style is in effect. Get uncached first line style based on
       // parent_first_line_style and cache the result in this object's style.
-      return StyleRef().AddCachedPseudoElementStyle(
-          GetUncachedPseudoElementStyle(kPseudoIdFirstLineInherited,
-                                        parent_first_line_style));
+      if (scoped_refptr<ComputedStyle> first_line_style =
+              GetUncachedPseudoElementStyle(kPseudoIdFirstLineInherited,
+                                            parent_first_line_style)) {
+        return StyleRef().AddCachedPseudoElementStyle(
+            std::move(first_line_style));
+      }
     }
   }
   return nullptr;