Changing slider values do not work properly when percent change of a step is less than one.

Source/modules/accessibility/AXNodeObject.cpp

Index: Source/modules/accessibility/AXNodeObject.cpp
diff --git a/Source/modules/accessibility/AXNodeObject.cpp b/Source/modules/accessibility/AXNodeObject.cpp
index c9294b0ff1f2039b98b16582f4c5c83e50ccc39a..ce4cabe26e0c52f53deb9e9685afd7ccfbd925a9 100644
--- a/Source/modules/accessibility/AXNodeObject.cpp
+++ b/Source/modules/accessibility/AXNodeObject.cpp
@@ -128,10 +128,20 @@ void AXNodeObject::alterSliderValue(bool increase)
     if (roleValue() != SliderRole)
         return;
 
-    if (!getAttribute(stepAttr).isEmpty())
-        changeValueByStep(increase);
-    else
-        changeValueByPercent(increase ? 5 : -5);
+    float value = valueForRange();
+    float step = stepValueForRange();

[dmazzoni, 2015/04/10 17:14:28]

It looks like stepValueForRange is implemented naively, it just returns the step
attribute.

I think better would be to get it from HTMLInputElement so that it follows the
spec correctly.

At first glance it looks like you should get it from
toHTMLInputElement(node())->createStepRange(RejectAny).step() (with appropriate
error checking, of course).

Yet another way to do it would be to try to set the value by the percentage, and
if it doesn't change, call HTMLInputElement::stepUp or stepDown.

+
+    if (getAttribute(stepAttr).isEmpty()) {
+        const float percentChange = 5;
+        float range = maxValueForRange() - minValueForRange();
+        step = range * (percentChange / 100);
+        if (step < 1)
+            step = 1;
+    }
+
+    value += increase ? step : -step;
+    setValue(String::number(value));
+    axObjectCache()->postNotification(node(), AXObjectCacheImpl::AXValueChanged);
 }
 
 String AXNodeObject::ariaAccessibilityDescription() const
@@ -155,18 +165,6 @@ void AXNodeObject::ariaLabeledByElements(WillBeHeapVector<RawPtrWillBeMember<Ele
         elementsFromAttribute(elements, aria_labelledbyAttr);
 }
 
-void AXNodeObject::changeValueByStep(bool increase)
-{
-    float step = stepValueForRange();
-    float value = valueForRange();
-
-    value += increase ? step : -step;
-
-    setValue(String::number(value));
-
-    axObjectCache()->postNotification(node(), AXObjectCacheImpl::AXValueChanged);
-}
-
 bool AXNodeObject::computeAccessibilityIsIgnored() const
 {
 #if ENABLE(ASSERT)
@@ -2077,15 +2075,4 @@ void AXNodeObject::ariaLabeledByText(Vector<AccessibilityText>& textOrder) const
     }
 }
 
-void AXNodeObject::changeValueByPercent(float percentChange)
-{
-    float range = maxValueForRange() - minValueForRange();
-    float value = valueForRange();
-
-    value += range * (percentChange / 100);
-    setValue(String::number(value));
-
-    axObjectCache()->postNotification(node(), AXObjectCacheImpl::AXValueChanged);
-}
-
 } // namespace blink