China is too busy dealing with the expansion of American influence around its borders right now. Plus, historically there hasn't been much hostilities between China and Russia except border skirmishes in disputed areas of the border (compare it with numerous bloody wars between Russia and various Western countries). The only Chinese leader who actively claimed Russian territory in recent history and could have attacked Russia was Mao Zedong. However, he is dead.
Unless hardcore nationalists take control of China, it won't try to restore control of Outer Manchuria.
Mao "could have attacked Russia", but not successfully. Mao was a bloated windbag who, through astonishing incompetence as a leader, caused the deaths of 45 million people (roughly the entire population of Spain, approximately 9 Scotlands) within 3 years in the "Great Leap Forward" and I don't even know how many in the Cultural Revolution. God knows how he would have screwed up an invasion of the USSR.
However, China has learned something that Russia has not; there are ways of challenging your rivals that do not necessarily involve outdated 20th century concepts like invading developed neighbours. Rather than some vague irredentist issue being drummed into relevance by the Secret Service for economic/political gain, China has other ways of making Russia dance to their tune. They've already got us dancing to their tune, I'll give them that.
Russian cities are already suffering from the effects of Russian government actions.
Mainiac, UR, I don't mean to make a big thing out of this but hear me out. If you say "heh" or use an emoticon like that after a sentence like that, what effect will it have? Why are you using it? It just seems like a snide, unpleasant thing to say. It's no laughing or smiling matter - Russia is in a terrible state right now and its people are being exploited by very powerful criminals whose influence runs right to the top. That's tragic, and the only thing that can change that is if ordinary Russian people become aware of that. How are you going to encourage ordinary Russians to see things from this perspective if you are snide or sarcastic? It's far more likely that you'll get a negative response and they'll switch off to your point of view.