[css-typed-om] Allow mutations of CSSTransformValues.

This patch allows CSSTransformValues items to be mutated/appended.
Spec issue here: https://github.com/w3c/css-houdini-drafts/issues/690

Bug: 545318
Change-Id: I841704e1f2ec8db0f27ae254a0949d4f9b46c8f7
Reviewed-on: https://chromium-review.googlesource.com/925882Reviewed-by: Darren Shen <shend@chromium.org>
Commit-Queue: nainar <nainar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537710}

third_party/WebKit/LayoutTests/external/wpt/css/css-typed-om/stylevalue-subclasses/cssTransformValue.tentative.html

@@ -25,6 +25,39 @@ test(() => {
   assert_style_value_array_equals(transform, values);
 }, 'CSSTransformValue can be constructed with multiple transforms');
 
+test(() => {
+  const values = [
+    new CSSScale(1, 1),
+    new CSSTranslate(CSS.px(1), CSS.px(1)),
+    new CSSRotate(CSS.deg(90))
+  ];
+
+  const transform = new CSSTransformValue(values);
+  assert_style_value_array_equals(transform, values);
+
+  values.pop();
+  var new_value = new CSSRotate(CSS.deg(45));
+  values[2] = new_value;
+  transform[2] = new_value;
+  assert_style_value_array_equals(transform, values);
+}, 'CSSTransformValue.set correctly sets the CSSTransformComponent at the given index');
+
+test(() => {
+  const values = [
+    new CSSScale(1, 1),
+    new CSSTranslate(CSS.px(1), CSS.px(1)),
+    new CSSRotate(CSS.deg(90))
+  ];
+
+  const transform = new CSSTransformValue(values);
+  assert_style_value_array_equals(transform, values);
+
+  var new_value = new CSSRotate(CSS.deg(45));
+  values[3] = new_value;
+  transform[3] = new_value;
+  assert_style_value_array_equals(transform, values);
+}, 'Setting a component in CSSTransformValue correctly appends the CSSTransformComponent if index specified is greater than length');
+
 test(() => {
   const transform = new CSSTransformValue([
     new CSSScale(1, 1),

third_party/WebKit/Source/core/css/cssom/CSSTransformValue.cpp

@@ -74,4 +74,25 @@ const CSSValue* CSSTransformValue::ToCSSValue() const {
   return transform_css_value;
 }
 
+bool CSSTransformValue::AnonymousIndexedSetter(
+    unsigned index,
+    const Member<CSSTransformComponent> component,
+    ExceptionState& exception_state) {
+  if (index < transform_components_.size()) {
+    transform_components_[index] = component;
+    return true;
+  }
+
+  if (index == transform_components_.size()) {
+    transform_components_.push_back(component);
+    return true;
+  }
+
+  exception_state.ThrowRangeError(
+      ExceptionMessages::IndexOutsideRange<unsigned>(
+          "index", index, 0, ExceptionMessages::kInclusiveBound,
+          transform_components_.size(), ExceptionMessages::kInclusiveBound));
+  return false;
+}
+
 }  // namespace blink

third_party/WebKit/Source/core/css/cssom/CSSTransformValue.h

@@ -38,9 +38,12 @@ class CORE_EXPORT CSSTransformValue final : public CSSStyleValue {
 
   StyleValueType GetType() const override { return kTransformType; }
 
-  CSSTransformComponent* componentAtIndex(uint32_t index) {
+  CSSTransformComponent* AnonymousIndexedGetter(uint32_t index) {
     return transform_components_.at(index);
   }
+  bool AnonymousIndexedSetter(unsigned,
+                              const Member<CSSTransformComponent>,
+                              ExceptionState&);
 
   size_t length() const { return transform_components_.size(); }
 

third_party/WebKit/Source/core/css/cssom/CSSTransformValue.idl

@@ -10,7 +10,8 @@
 ] interface CSSTransformValue : CSSStyleValue {
     // https://github.com/w3c/css-houdini-drafts/issues/358
     readonly attribute unsigned long length;
-    [ImplementedAs=componentAtIndex] getter CSSTransformComponent (unsigned long index);
+    getter CSSTransformComponent (unsigned long index);
+    [RaisesException] setter CSSTransformComponent (unsigned long index, CSSTransformComponent val);
     iterable<CSSTransformComponent>;
 
     readonly attribute boolean is2D;