src/vs/editor/common/viewModel/viewModelDecorations.ts/ViewModelDecorations/getDecorationsViewportData
class ViewModelDecorations:	public getDecorationsViewportData(viewRange: Range): IDecorationsViewportData {
		let cacheIsValid = (this._cachedModelDecorationsResolver !== null);
		cacheIsValid = cacheIsValid && (viewRange.equalsRange(this._cachedModelDecorationsResolverViewRange));
		if (!cacheIsValid) {
			this._cachedModelDecorationsResolver = this._getDecorationsViewportData(viewRange);
			this._cachedModelDecorationsResolverViewRange = viewRange;
		}
		return this._cachedModelDecorationsResolver!;
	}