Bug 699325: Make calcMode="paced" smil animation fall back to calcMode="discrete" when its values have 0 distance between them. r=birtles

content/smil/crashtests/699325-1.svg

@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg">
+  <rect fill="blue" height="100" width="100">
+    <animate id="a" attributeName="x"  calcMode="paced" values="50; 50; 50"/>
+  </rect>
+</svg>

content/smil/crashtests/crashtests.list

@@ -42,3 +42,4 @@ load 670313-1.svg
 load 678822-1.svg
 load 678847-1.svg
 load 678938-1.svg
+load 699325-1.svg

content/smil/nsSMILAnimationFunction.cpp

@@ -561,6 +561,13 @@ nsSMILAnimationFunction::ComputePacedPosition(const nsSMILValueArray& aValues,
   if (totalDistance == COMPUTE_DISTANCE_ERROR)
     return NS_ERROR_FAILURE;
 
+  // If we have 0 total distance, then it's unclear where our "paced" position
+  // should be.  We can just fail, which drops us into discrete animation mode.
+  // (That's fine, since our values are apparently indistinguishable anyway.)
+  if (totalDistance == 0.0) {
+    return NS_ERROR_FAILURE;
+  }
+
   // total distance we should have moved at this point in time.
   // (called 'remainingDist' due to how it's used in loop below)
   double remainingDist = aSimpleProgress * totalDistance;