For searching Hangout history. Click gRewind once to scroll up. Click again to stop scrolling. Then use Command/Control+F to search.
Annoyed by how Gmail now lazy-loads your chat history and looking for a particular line of text? Click Chats on the left sidebar and open your latest Hangout with a user. Click gRewind once to scroll history up. Click again to stop scrolling. Then use Control+F (or Command+F on a Mac) to search.