Update the AudioParam value attribute correctly from timelines.

third_party/WebKit/LayoutTests/webaudio/resources/audio-param.js

+// Define functions that implement the formulas for AudioParam automations.
+
+// AudioParam linearRamp value at time t for a linear ramp between (t0, v0) and (t1, v1).  It is
+// assumed that t0 <= t.  Results are undefined otherwise.
+function audioParamLinearRamp(t, v0, t0, v1, t1)
+{
+    if (t >= t1)
+        return v1;
+    return (v0 + (v1 - v0) * (t - t0) / (t1 - t0))
+}
+
+// AudioParam exponentialRamp value at time t for an exponential ramp between (t0, v0) and (t1, v1).
+// It is assumed that t0 <= t.  Results are undefined otherwise.
+function audioParamExponentialRamp(t, v0, t0, v1, t1)
+{
+    if (t >= t1)
+        return v1;
+    return v0 * Math.pow(v1 / v0, (t - t0) / (t1 - t0));
+}
+
+// AudioParam setTarget value at time t for a setTarget curve starting at (t0, v0) with a final
+// value of vFainal and a time constant of timeConstant.  It is assumed that t0 <= t.  Results are
+// undefined otherwise.
+function audioParamSetTarget(t, v0, t0, vFinal, timeConstant)
+{
+    return vFinal + (v0 - vFinal) * Math.exp(-(t - t0) / timeConstant);
+}
+
+// AudioParam setValueCurve value at time t for a setValueCurve starting at time t0 with curve,
+// curve, and duration duration.  The sample rate is sampleRate.  It is assumed that t0 <= t.
+function audioParamSetValueCurve(t, curve, t0, duration)
+{
+    if (t > t0 + duration)
+        return curve[curve.length - 1];
+
+    var curvePointsPerSecond = (curve.length - 1) / duration;
+
+    var virtualIndex = (t - t0) * curvePointsPerSecond;
+    var index = Math.floor(virtualIndex);
+
+    var delta = virtualIndex - index;
+
+    var c0 = curve[index];
+    var c1 = curve[Math.min(index + 1, curve.length - 1)];
+    return c0 + (c1 - c0) * delta;
+}