Using "AssetDatabase.CopyAsset" function takes too much memory for every copied asset. If the assets are enough to take all the system memory, the Editor crashes which is user's real case.

Steps to reproduce:
1. Open user's attached project
2. Go to menu Test > CopyTextures.
3. Look in the Activity Monitor app (or any other memory tracker) that there are massive memory growths.

Result: a lot of memory is being used, if it takes all the system memory, the Editor crashes.

Reproduced with: 2017.2.0b9, 2017.1.0p5, 5.6.3p2.
Not reproduced with: 5.5.4p2.
Regression introduced in: 5.6.2p1.

Workaround: use FileUtil.CopyFileOrDirectory(srcPath, dstPath);

Note: not reproducible on Windows.