Slider NG: Move SliderPosition() to HTMLInputElement

This CL makes SliderPosition() in layout_slider_track.cc a method of
blink::HTMLInputElement. This change will help to share the code
between the legacy layout and LayoutNG.

This CL has no behavior changes.

Bug: 1040826
Change-Id: I65bb04e8808820a812a4fabb82a7bf24c5f66341
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417780
Auto-Submit: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808240}

third_party/blink/renderer/core/html/forms/html_input_element.cc

@@ -1264,6 +1264,14 @@ void HTMLInputElement::setValueAsNumber(double new_value,
   input_type_->SetValueAsDouble(new_value, event_behavior, exception_state);
 }
 
+Decimal HTMLInputElement::RatioValue() const {
+  DCHECK_EQ(type(), input_type_names::kRange);
+  const StepRange step_range(CreateStepRange(kRejectAny));
+  const Decimal old_value =
+      ParseToDecimalForNumberType(value(), step_range.DefaultValue());
+  return step_range.ProportionFromValue(step_range.ClampValue(old_value));
+}
+
 void HTMLInputElement::SetValueFromRenderer(const String& value) {
   // File upload controls will never use this.
   DCHECK_NE(type(), input_type_names::kFile);

third_party/blink/renderer/core/html/forms/html_input_element.h

@@ -174,6 +174,11 @@ class CORE_EXPORT HTMLInputElement
       ExceptionState&,
       TextFieldEventBehavior = TextFieldEventBehavior::kDispatchNoEvent);
 
+  // For type=range, returns a ratio of the current value in the range between
+  // min and max.  i.e. (value - min) / (max - min)
+  // For other types, this function fails with DCHECK().
+  Decimal RatioValue() const;
+
   String ValueOrDefaultLabel() const;
 
   // This function dispatches 'input' event for non-textfield types. Callers

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

@@ -33,9 +33,7 @@
 
 #include "third_party/blink/renderer/core/dom/shadow_root.h"
 #include "third_party/blink/renderer/core/html/forms/html_input_element.h"
-#include "third_party/blink/renderer/core/html/forms/slider_thumb_element.h"
 #include "third_party/blink/renderer/core/html/forms/slider_track_element.h"
-#include "third_party/blink/renderer/core/html/parser/html_parser_idioms.h"
 #include "third_party/blink/renderer/core/html/shadow/shadow_element_names.h"
 
 namespace blink {
@@ -43,13 +41,6 @@ namespace blink {
 LayoutSliderTrack::LayoutSliderTrack(SliderTrackElement* element)
     : LayoutBlockFlow(element) {}
 
-inline static Decimal SliderPosition(HTMLInputElement* element) {
-  const StepRange step_range(element->CreateStepRange(kRejectAny));
-  const Decimal old_value =
-      ParseToDecimalForNumberType(element->value(), step_range.DefaultValue());
-  return step_range.ProportionFromValue(step_range.ClampValue(old_value));
-}
-
 void LayoutSliderTrack::UpdateLayout() {
   auto* input = To<HTMLInputElement>(GetNode()->OwnerShadowHost());
   const bool is_vertical = !StyleRef().IsHorizontalWritingMode();
@@ -73,7 +64,7 @@ void LayoutSliderTrack::UpdateLayout() {
   if (!thumb)
     return;
 
-  double percentage_offset = SliderPosition(input).ToDouble();
+  double percentage_offset = input->RatioValue().ToDouble();
   LayoutUnit available_extent = is_vertical ? ContentHeight() : ContentWidth();
   available_extent -=
       is_vertical ? thumb->Size().Height() : thumb->Size().Width();