In this era we need to move to the idea of "effective monopolies". Just because Chrome isn't an absolute monopoly, doesn't mean it can't essentially dictate whatever direction it wants in a mostly unchecked manner.
Even American "monopoly" legislation, and our horrible "only care about the consumer" opinion on monopolies has ALWAYS supported breaking up companies that don't have 100% of the industry because they do anti-consumer shit with whatever percentage control they have.