Roll Observatory deps (charted -> ^0.3.0)

packages/charted/lib/core/scales/linear_scale.dart

Index: packages/charted/lib/core/scales/linear_scale.dart
diff --git a/packages/charted/lib/core/scales/linear_scale.dart b/packages/charted/lib/core/scales/linear_scale.dart
index a0de8fb6c4c980259d4bd58807f1bf641a355410..4c983dce7005e11152a5e15ebcad72011c9b12d3 100644
--- a/packages/charted/lib/core/scales/linear_scale.dart
+++ b/packages/charted/lib/core/scales/linear_scale.dart
@@ -40,15 +40,15 @@ class LinearScale implements Scale {
           _domain, ScaleUtils.niceStep(_linearTickRange().step));
     }
 
-    Function linear = math.min(_domain.length, _range.length) > 2 ?
-        ScaleUtils.polylinearScale : ScaleUtils.bilinearScale;
+    Function linear = math.min(_domain.length, _range.length) > 2
+        ? ScaleUtils.polylinearScale
+        : ScaleUtils.bilinearScale;
 
     Function uninterpolator = clamp ? uninterpolateClamp : uninterpolateNumber;
     InterpolatorGenerator interpolator =
         _rounded ? createRoundedNumberInterpolator : createNumberInterpolator;
 
-    _invert =
-        linear(_range, _domain, uninterpolator, createNumberInterpolator);
+    _invert = linear(_range, _domain, uninterpolator, createNumberInterpolator);
     _scale = linear(_domain, _range, uninterpolator, interpolator);
   }
 
@@ -135,19 +135,19 @@ class LinearScale implements Scale {
     if (extent == null) {
       extent = ScaleUtils.extent(_domain);
     }
-    var span = extent.max - extent.min,
-        step =
-            math.pow(10, (math.log(span / _ticksCount) / math.LN10).floor()),
-        err = _ticksCount / span * step;
+    var span = extent.max - extent.min;
+    if (span == 0) {
+      span = 1.0; // [span / _ticksCount] should never be equal zero.
+    }
+    var step = math.pow(10, (math.log(span / _ticksCount) / math.LN10).floor());
+    var err = _ticksCount / span * step;
 
     // Filter ticks to get closer to the desired count.
     if (err <= .15) {
       step *= 10;
-    }
-    else if (err <= .35) {
+    } else if (err <= .35) {
       step *= 5;
-    }
-    else if (err <= .75) {
+    } else if (err <= .75) {
       step *= 2;
     }