Adds some useful hotkeys to the Animation window in Unity.

UnityAnimationWindowHotkeys.cs

// Tested on Unity 5.3.5 & Unity 5.5.1
using UnityEngine;
using UnityEditor;
using UnityEditorInternal;
using System.Collections;
using System.Reflection;

[ExecuteInEditMode]
public class AnimationWindowHotkeys : Editor
{
	static System.Type animWindowType = null;
	static System.Type animEditorType = null;

	static System.Type GetAnimationWindowType() 
	{
		if( animWindowType == null )
		{
			animWindowType = System.Type.GetType( "UnityEditor.AnimationWindow,UnityEditor" );
		}
		return animWindowType;
	}

	static System.Type GetAnimEditorType() 
	{
		if( animEditorType == null )
		{
			animEditorType = System.Type.GetType( "UnityEditor.AnimEditor,UnityEditor" );
		}
		return animEditorType;		
	}

	static Object GetAnimationWindow() 
	{
		Object[] openAnimationWindows = Resources.FindObjectsOfTypeAll(GetAnimationWindowType ());
		if ( openAnimationWindows.Length > 0 ) 
		{
			return openAnimationWindows[0];
		}
		return null;
	}

	static object GetAnimEditor() 
	{
		var wndType = GetAnimationWindowType ();

		Object[] openAnimationWindows = Resources.FindObjectsOfTypeAll(wndType);
		if ( openAnimationWindows.Length > 0 ) 
		{
			return wndType.GetField("m_AnimEditor", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(openAnimationWindows[0]);
		}
		return null;
	}

	static void RepaintAnimationWindow() 
	{
		Object w = GetAnimationWindow();
		if ( w != null ) 
		{
			( w as EditorWindow ).Repaint();
		}
	}

	[MenuItem( "GlobalHotKeys/Animation/Prev Keyframe #," )]
	static void PrevFrame() 
	{
		var w = GetAnimEditorType().GetField("m_State", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(GetAnimEditor());
		if (w != null) 
		{
			var t = w.GetType();
			var p = t.GetProperty("frame", BindingFlags.Instance | BindingFlags.Public);

			var v = (int)p.GetValue(w, new object[]{ });

			if (v <= 0)
				return;

			p.SetValue (w, v - 1, new object[] { });
			RepaintAnimationWindow();
		}
	}

	[MenuItem( "GlobalHotKeys/Animation/Next Keyframe #." )]
	static void NextFrame() 
	{
		var w = GetAnimEditorType().GetField("m_State", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(GetAnimEditor());
		if (w != null) 
		{
			var t = w.GetType();
			var p = t.GetProperty("frame", BindingFlags.Instance | BindingFlags.Public);

			var v = (int)p.GetValue(w, new object[]{ });
			p.SetValue (w, v + 1, new object[] { });
			RepaintAnimationWindow();
		}
	}

	[MenuItem( "GlobalHotKeys/Animation/Prev Keyframe &," )]
	static void PrevKeyframe() 
	{
		var w = GetAnimEditor();
		if ( w != null )
		{
			GetAnimEditorType().InvokeMember( "MoveToPreviousKeyframe", BindingFlags.InvokeMethod | BindingFlags.NonPublic, null, w, null );
			RepaintAnimationWindow();
		}
	}

	[MenuItem( "GlobalHotKeys/Animation/Next Keyframe &." )]
	static void NextKeyframe() 
	{
		var w = GetAnimEditor();
		if ( w != null )
		{
			GetAnimEditorType().InvokeMember( "MoveToNextKeyframe", BindingFlags.InvokeMethod | BindingFlags.NonPublic, null, w, null );
			RepaintAnimationWindow();
		}
	}
}