It seems nobody really noticed this so Google is bringing out the news via a new blog post. The search giant says this new optimization technique speeds up operation by using data from runtime execution to track which functions are most commonly used, so they can optimize these functions for higher performance:
To gather this data, the nightly build process now produces a special version of Chrome that tracks how often functions are used. PGO then optimizes those high-use functions for speed, in some cases increasing the binary size of those functions. To balance out that increase, PGO also optimizes less-used functions with smaller, though slightly slower code. These trade-offs result in higher overall performance, and a smaller overall code footprint.The result is that on average, the Windows version of Chrome now starts 16.8 percent faster, loads new tabs 14.8 percent faster and loads pages 5.9 percent faster.
PGO also optimizes the memory location of the code, moving rarely-used functions away from frequently-used ones in memory. This results in more optimal use of the CPU instruction cache by avoiding caching of less-used code, increasing overall performance. There are many other tricks that PGO uses to make Chrome faster, and they add up to great results.