Skip computing SMIL underlying value if not used

If the first animation in the sandwich does not depend on the underlying
value we can avoid computing it - which for certain types can avoid
flushing style.

Bug: 981355
Change-Id: Ic15e863f03f8f7194eea9a453b980f416f1bff37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2403263Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#805798}

third_party/blink/renderer/core/svg/animation/smil_animation_sandwich.cc

@@ -93,23 +93,26 @@ bool SMILAnimationSandwich::ApplyAnimationValues() {
   if (!result_element)
     return false;
 
-  // Only reset the animated type to the base value once for
-  // the lowest priority animation that animates and
-  // contributes to a particular element/attribute pair.
-  result_element->ResetAnimatedType();
-
   // Animations have to be applied lowest to highest prio.
   //
   // Only calculate the relevant animations. If we actually set the
   // animation value, we don't need to calculate what is beneath it
   // in the sandwich.
+  bool needs_underlying_value = true;
   auto* sandwich_start = active_.end();
   while (sandwich_start != active_.begin()) {
     --sandwich_start;
-    if ((*sandwich_start)->OverwritesUnderlyingAnimationValue())
+    if ((*sandwich_start)->OverwritesUnderlyingAnimationValue()) {
+      needs_underlying_value = false;
       break;
+    }
   }
 
+  // Only reset the animated type to the base value once for
+  // the lowest priority animation that animates and
+  // contributes to a particular element/attribute pair.
+  result_element->ResetAnimatedType(needs_underlying_value);
+
   for (auto* sandwich_it = sandwich_start; sandwich_it != active_.end();
        sandwich_it++) {
     (*sandwich_it)->ApplyAnimation(result_element);

third_party/blink/renderer/core/svg/svg_animate_element.cc

@@ -432,7 +432,7 @@ bool SVGAnimateElement::CalculateFromAndByValues(const String& from_string,
   return true;
 }
 
-void SVGAnimateElement::ResetAnimatedType() {
+void SVGAnimateElement::ResetAnimatedType(bool needs_underlying_value) {
   DCHECK(targetElement());
   if (IsAnimatingSVGDom()) {
     // SVG DOM animVal animation code-path.
@@ -447,7 +447,9 @@ void SVGAnimateElement::ResetAnimatedType() {
 
   // CSS properties animation code-path.
   String base_value =
-      ComputeCSSPropertyValue(targetElement(), css_property_id_);
+      needs_underlying_value
+          ? ComputeCSSPropertyValue(targetElement(), css_property_id_)
+          : g_empty_string;
   animated_value_ = CreatePropertyForAnimation(base_value);
 }
 

third_party/blink/renderer/core/svg/svg_animate_element.h

@@ -59,7 +59,7 @@ class CORE_EXPORT SVGAnimateElement : public SVGAnimationElement {
 
   bool HasValidAnimation() const override;
 
-  void ResetAnimatedType() final;
+  void ResetAnimatedType(bool needs_underlying_value) final;
   void ClearAnimatedType() final;
 
   bool CalculateToAtEndOfDurationValue(

third_party/blink/renderer/core/svg/svg_animate_motion_element.cc

@@ -153,7 +153,7 @@ static bool ParsePoint(const String& string, FloatPoint& point) {
   });
 }
 
-void SVGAnimateMotionElement::ResetAnimatedType() {
+void SVGAnimateMotionElement::ResetAnimatedType(bool needs_underlying_value) {
   SVGElement* target_element = targetElement();
   DCHECK(target_element);
   DCHECK(TargetCanHaveMotionTransform(*target_element));

third_party/blink/renderer/core/svg/svg_animate_motion_element.h

@@ -42,7 +42,7 @@ class SVGAnimateMotionElement final : public SVGAnimationElement {
 
   void ParseAttribute(const AttributeModificationParams&) override;
 
-  void ResetAnimatedType() override;
+  void ResetAnimatedType(bool needs_underlying_value) override;
   void ClearAnimatedType() override;
   bool CalculateToAtEndOfDurationValue(
       const String& to_at_end_of_duration_string) override;

third_party/blink/renderer/core/svg/svg_animation_element.h

@@ -71,7 +71,7 @@ class CORE_EXPORT SVGAnimationElement : public SVGSMILElement {
   DEFINE_ATTRIBUTE_EVENT_LISTENER(end, kEndEvent)
   DEFINE_ATTRIBUTE_EVENT_LISTENER(repeat, kRepeatEvent)
 
-  virtual void ResetAnimatedType() = 0;
+  virtual void ResetAnimatedType(bool needs_underlying_value) = 0;
   virtual void ClearAnimatedType() = 0;
   virtual void ApplyResultsToTarget() = 0;
   // Returns true if this animation "sets" the value of the animation. Thus all