Don't EnsureComputedStyle in LayoutTextControlSingleLine.

We do have a LayoutObject for the spinner which means we have a
ComputedStyle already.

Also added some documentation to EnsureComputedStyle for <area>.

Bug: 895894
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ie0ee5c75fae0f699721a30f3072eec526c50083e
Reviewed-on: https://chromium-review.googlesource.com/c/1286412
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600600}

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

@@ -244,10 +244,10 @@ LayoutUnit LayoutTextControlSingleLine::PreferredContentLogicalWidth(
     if (LayoutBox* spin_layout_object =
             spin_button ? spin_button->GetLayoutBox() : nullptr) {
       result += spin_layout_object->BorderAndPaddingLogicalWidth();
-      // Since the width of spinLayoutObject is not calculated yet,
-      // spinLayoutObject->logicalWidth() returns 0.
-      // So ensureComputedStyle()->logicalWidth() is used instead.
-      result += spin_button->EnsureComputedStyle()->LogicalWidth().Value();
+      // Since the width of spin_layout_object is not calculated yet,
+      // spin_layout_object->LogicalWidth() returns 0. Use the computed logical
+      // width instead.
+      result += spin_layout_object->StyleRef().LogicalWidth().Value();
     }
   }
 

third_party/blink/renderer/core/paint/image_painter.cc

@@ -52,6 +52,8 @@ void ImagePainter::PaintAreaElementFocusRing(const PaintInfo& paint_info) {
   // do it for an area within an image, so we don't call
   // LayoutTheme::themeDrawsFocusRing here.
 
+  // We use EnsureComputedStyle() instead of GetComputedStyle() here because
+  // <area> is used and its style applied even if it has display:none.
   const ComputedStyle& area_element_style = *area_element.EnsureComputedStyle();
   // If the outline width is 0 we want to avoid drawing anything even if we
   // don't use the value directly.