View.measure throws error due to difference in _privateFlags handling from JavaScriptCore ios-runtime

[NathanWalker]

From core modules view.ios.js:

View.prototype.measure = function (widthMeasureSpec, heightMeasureSpec) {
        var measureSpecsChanged = this._setCurrentMeasureSpecs(widthMeasureSpec, heightMeasureSpec);
        var forceLayout = (this._privateFlags & PFLAG_FORCE_LAYOUT) === PFLAG_FORCE_LAYOUT;
        if (forceLayout || measureSpecsChanged) {
            this._privateFlags &= ~PFLAG_MEASURED_DIMENSION_SET;
            this.onMeasure(widthMeasureSpec, heightMeasureSpec);
            this._privateFlags |= PFLAG_LAYOUT_REQUIRED;
            if ((this._privateFlags & PFLAG_MEASURED_DIMENSION_SET) !== PFLAG_MEASURED_DIMENSION_SET) {
                throw new Error("onMeasure() did not set the measured dimension by calling setMeasuredDimension() " + this);
            }
        }
    };

The throw new Error will occur with latest v8 runtime whereas with JSC runtime never occurs. I suspect this has something to do with _privateFlags handling? Perhaps JSC runtime is assisting with something here which is not yet present in v8 runtime?

Repro: I will demonstrate in a project (not sure exactly what conditions give rise to it) but can say that with JSC runtime the throw never occurs under same circumstances.