Moved SVG check for ::first-letter to CanGeneratePseudoElement.

Was currently just checked when trying to create the pseudo element.
This change should have no effect, but is done in preparation for [1].

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1155591

Bug: 847218
Change-Id: I99fa06bed1256cb6405e6f24a5f116def366acf9
Reviewed-on: https://chromium-review.googlesource.com/1156389Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579376}

third_party/blink/renderer/core/dom/element.cc

@@ -4009,8 +4009,6 @@ PseudoElement* Element::CreatePseudoElementIfNeeded(PseudoId pseudo_id) {
   if (!CanGeneratePseudoElement(pseudo_id))
     return nullptr;
   if (pseudo_id == kPseudoIdFirstLetter) {
-    if (IsSVGElement())
-      return nullptr;
     if (!FirstLetterPseudoElement::FirstLetterTextLayoutObject(*this))
       return nullptr;
   }
@@ -4128,6 +4126,8 @@ scoped_refptr<ComputedStyle> Element::StyleForPseudoElement(
 bool Element::CanGeneratePseudoElement(PseudoId pseudo_id) const {
   if (pseudo_id == kPseudoIdBackdrop && !IsInTopLayer())
     return false;
+  if (pseudo_id == kPseudoIdFirstLetter && IsSVGElement())
+    return false;
   if (const ComputedStyle* style = GetComputedStyle())
     return style->CanGeneratePseudoElement(pseudo_id);
   return false;