What are these abilities that allow moving at full speed using acrobatics?

Question

In the skill description for acrobatics in the section about moving through threatened squares, it states that there are abilities that allow you to move through at full speed:

Move Through Threatened Squares

In addition, you can move through a threatened square without provoking an attack of opportunity from an enemy by using Acrobatics. When moving in this way, you move at half speed. You can move at full speed by increasing the DC of the check by 10. You cannot use Acrobatics to move past foes if your speed is reduced due to carrying a medium or heavy load or wearing medium or heavy armor. If an ability allows you to move at full speed under such conditions, you can use Acrobatics to move past foes. You can use Acrobatics in this way while prone, but doing so requires a full-round action to move 5 feet, and the DC is increased by 5. If you attempt to move through an enemy’s space and fail the check, you lose the move action and provoke an attack of opportunity.

What are the abilities it's talking about? Is there a feat a gunslinger could take to get this ability?

Answer 1

Some common abilities that work in this instance:

As Ling pointed out, the Dwarves' Slow and Steady racial trait:

Base Speed: (Slow and Steady) Dwarves have a base speed of 20 feet, but their speed is never modified by armor or encumbrance.

Commonly also a Fighter's Armor Training:

Armor Training (Ex) Starting at 3rd level, a fighter learns to be more maneuverable while wearing armor. ...a fighter can also move at his normal speed while wearing medium armor. At 7th level, a fighter can move at his normal speed while wearing heavy armor.

Finally, the spell Effortless Armor:

Armor you wear no longer reduces your speed.

There are more abilities that can do this, but these are the most common ones.

Answer 2

One ability that I know of.

From the racial entry for Dwarves:

Base Speed: (Slow and Steady) Dwarves have a base speed of 20 feet, but their speed is never modified by armor or encumbrance.