First, a few points about your question. Rank 25-20 is very easy. I would not give much credence to your performance in those ranks. Second, losing 5 games in a row could just as easily be bad luck. What matters is your performance in the long run.
Most legendaries alone will not swing a game, or simply require dumb luck to do so. There are also a relatively limited pool of legendaries that you'll come across. Learn what those are. Here's how I deal with them:
Save removal
Save your counters and other cards as best you can. Playing against a secret paladin? Save your counters for the very likely Tirion. They are probably holding on to him waiting for you to burn your removal cards.
Ignore it
If you can gain tempo early and maintain board control, there's a very good chance that by the time your opponent plays a legendary it will be too little, too late. Most of the time if your opponent plays a legendary and you lose, there's a good chance you were already losing anyway. Outside of some really good luck (a lucky Ragnaros hit) most legendaries aren't enough to immediately swing a game.
Win before it's a problem
Most legendaries are high cost cards. Focus on decks that will let you win before they even get a chance to play them, such as variations of Zoo decks that focus on lots of low cost minions. This ties into my previous point, gain tempo and board control early.
Conclusion
It's entirely possible you'll lose a game due to a crucial legendary card from your opponent and there was absolutely nothing you could have done to avoid it. It'll happen. A single game means nothing aside from tournaments. Focus on your play and strategy. Legendaries are powerful, but they alone can not win a game. More often it was not the legendary you lost to, but the other cards and good plays that aren't as flashy. You just remember the legendary.
On a generalized level, you're asking how to beat something that counters aggresive decks, while playing aggresive decks. Which, in a 'perfect' world, shouldn't happen.
I do have two sidepoints before talking about the extremely advanced aggresive tactics you can use;
1. Alternative
Since you just asked about "aggresive decks", and not your specific rogue deck, I believe Tempo Mage can do well against control warrior, but it's not the ultra aggresive deck (unless you get perfect wyrmWyrmCoinMirror (counter weps) + cheap spells opener) - Maybe Mana Addict would make it more aggresive.
2. Survive to live another day
You didn't mention anything about rank - If rank is irrelevant to you, the easiest solution is to just concede and quickly get to the next fight. Honestly, it's the best option against any deck that just intends to prolong the game forever! It's better to get 2-3 games with decent probability of winning, than hoping you might win that one game.
.
To answer the "main point" of your question... What strategies to use?
Go face.
Hard.
Go more face.
And hope he doesn't have brawl.
Honestly, unless you dominate the board, his face AND he doesn't have aoe, you shouldn't win. You need him to draw bad.
... If someone has a better reliable strategy, I'd LOVE to hear it.
Best Answer
Cards to consider adding vs aggro decks:
1 Blizzard - I would highly recommend you put these in, due to the fact that they both freeze all your opponent's minions, AND do 2 damage to all of them, killing a large number of aggro creatures and stalling others.
2 Vaporize - If you're keeping the board clear of smaller minions, this'll help you take care of bigger minions if used properly.
1 Arcane Missiles - Can 2 for 1 against aggro rush decks, assist in taking down 2 toughness or greater minions. Cons - Based on RNG.
2 Mirror Image AND/OR 2 Ice Barrier AND/OR 2 Frost Nova - One of the biggest counters to an aggro deck is stalling it out, especially in a Mage deck where you can pull a turn 7 flamestrike. These 3 cards are all excellent for stalling, as Mirror Image basically prevents 2 creatures from doing damage, even charge creatures, Ice Barrier, being a secret, can cause your opponent to play abnormally, such as playing a smaller minion than they would have because they're afraid of Mirror Entity. In addition, it basically heals you 8, even if you're at full health, which is pretty solid vs an aggro deck. Frost Nova is likely the weakest at stalling an aggro deck, due to not effecting charge minions at all, but is more relevant typically late game, due to effecting all of your opponents minions out currently.
2 Cone of Cold - While Arcane Explosion is generally considered a bad card, Cone of Cold is relevant at times, due to the fact that those minions it doesn't kill with it's 1 damage will still be frozen for a turn, making it still a relevant card in the late game.
Cards to change out:
1 Gadgetzan Auctioneer -> 1 Acolyte of Pain - Gadgetzan Auctioneer isn't necessarily guaranteed to draw you a card when you play it, and is a high costing 5 drop, with not very high toughness. Alternatively, Acolyte of Pain is almost always guaranteed to draw you a card, unless silenced or straight up destroyed, and, when combined with your hero power, will be able to trade for 2 toughness or less creatures well.
1 Argent Squire -> 1 Mana Wyrm - Mana Wyrm is one of the best 1 drop minions in the game, very often 2 for 1's, or at the very least, trades up. Argent Squire CAN 2 for 1, but only against 1 toughness creatures. In addition, it doesn't have ANY impact late game, whereas a mana wyrm can.
Cards to consider taking out:
1 Sunfury Protector - While not the worst card, this is the kind of card that doesn't really do anything unless you have other cards to go with it. In this case, those other cards happen to be minions. When combined with a Chillwind Yeti, or better yet, a boulderfist ogre, it can be very powerful, but without one of those, it doesn't necessarily do much. If you still like the synergy of it with minions such as these, I would recommend replacing it with Defender of Argus, as you're almost never going to be playing Sunfury Protector before turn 5 or so anyways, and Defender of Argus is more relevant with minions such as Acolyte of Pain and Mana Wyrm
1 Azure Drake AND/OR 2 Boulderfist Ogres - If Aggro decks are really your only weakness, I would consider removing some of these more expensive creatures. Boulderfist Ogre is particularly useless against aggro decks, because they will just proceed to ignore your ogre, since they likely have you far lower at the point you play it than you do them, and you can only use it to kill one minion of theirs a turn.