TextDecorationInfo only allocated on the stack

Mark it as STACK_ALLOCATED. There's a ComputedStyle which is not
refcounted which would be dangerous if TextDecorationInfo gets allocated
on the heap.

Noticed this when reviewing moving ComputedStyle to Oilpan.

Change-Id: Ia3ec8ea0bfa542da817110d6c1b9b6c52315ad21
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2637834Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844769}

third_party/blink/renderer/core/paint/text_decoration_info.h

@@ -33,6 +33,8 @@ enum class ResolvedUnderlinePosition {
 // invalidation and painting. See also
 // https://www.w3.org/TR/css-text-decor-3/#painting-order
 class CORE_EXPORT TextDecorationInfo {
+  STACK_ALLOCATED();
+
  public:
   TextDecorationInfo(
       const PhysicalOffset& box_origin,