This is false! Yes, dogs were domesticated from wolves thousands of years ago, and then selectively bred by humans for desired sizes, shapes, and characteristics. However, they have NOT adapted to a cooked food diet, as evidenced by the millions of pets sitting in the waiting rooms of veterinary clinics with periodontal disease, skin diseases, cancers, organ diseases, diabetes, obesity—diseases that have strong connections to cooked and processed foods. No, a cooked diet has not been kind to our animals.
Kibbled foods (which are cooked and highly processed) have only been around for the last 100 years. Evolutionary adaptations require much more time than this. The evolutionary changes—from gross anatomy down to the molecular level—that would be required for the development of such different digestive capabilities would take MUCH longer than the time that wolves have been living with humans.
So what were pets eating before the advent of cooked, processed, kibbled pet diets? They received hardly any cooked food, as food was a precious commodity that very few people would waste on something like a dog (remember, dogs have not always enjoyed the same social status they enjoy now). Instead, they received the human "waste food"—things people would not use or eat, which may have included a small portion of table scraps. By and large, however, the dogs foraged and scavenged on their own, or hunted small prey animals to supplement what little food they received at home.
And before this? Wolf-dogs hunted with their masters and hung around the camps, knowing they would receive whatever raw meat, bones, and offal were left over (Feldhamer, G.A. 1999. Mammology: Adaptation, Diversity, and Ecology. McGraw-Hill. pg 472.). Thousands of years ago, people did not cook for their pets. Why should they? The animals were fully capable of obtaining their own food and moreover were a good "disposal" for unused parts of animals. The dogs ate what they were designed to eat, and until the 1950s (some argue as late as the 1980s and 1990s), dogs were recognized as the carnivores they are.
For more about why home-made, cooked food diets are not a completely viable alternative to raw, please read the Cooked Food myth.