Add size warning for NGInlineItem

As a preparation to add |NGTextType| to |NGInlineItem|.

This patch has no behavior changes.

Bug: 982194
Change-Id: Iec07f6606458fe16a1fe2d3f0e16a2069944af46
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153459Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Auto-Submit: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759978}

third_party/blink/renderer/core/layout/ng/inline/ng_inline_item.cc

@@ -12,6 +12,15 @@
 namespace blink {
 namespace {
 
+struct SameSizeAsNGInlineItem {
+  void* pointers[2];
+  unsigned integers[3];
+  unsigned bit_fields : 32;
+};
+
+static_assert(sizeof(NGInlineItem) == sizeof(SameSizeAsNGInlineItem),
+              "NGInlineItem should stay small");
+
 const char* kNGInlineItemTypeStrings[] = {
     "Text",     "Control",  "AtomicInline",        "OpenTag",
     "CloseTag", "Floating", "OutOfFlowPositioned", "BidiControl"};