Check your References for Microsoft.VisualStudio.QualityTools.CodedUITestFramework, and also your using block for using Microsoft.VisualStudio.TestTools.UITesting;
If those don't exist, first add the using statement, then rebuild your solution. If you are still having the error, right click on References -> Add Reference. Then search for Microsoft.VisualStudio.QualityTools.CodedUITestFramework.dll. If it doesn't come up in the list, click Browse and navigate to where the .dll is located. For me it's C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\PublicAssemblies\Microsoft.VisualStudio.QualityTools.CodedUITestFramework.dll. Select the .dll -> click Add -> Ok, then rebuild your solution again.
If you create a solution with Unit Test Project (or anything other than CodedUI Test Project), then you need to add the .dll and using statement.