On Linux, this accelerator key combo can be used to move tabs left or right in the tab strip, which is extremely useful. On Windows, there doesn't seem to be any accelerator key combo that works.

Also, on Mac, I'd expect the standard CMD+SHIFT+'{' (or '}') accelerator would do the trick just like in all other apps with tabs (such as Terminal). However, it seems like we just switch tabs (same behavior as CMD+'{') instead of moving the current tab. We should fix this.

The code that acts on accelerator commands and calls MoveTabNext/Previous() is here: https://cs.chromium.org/chromium/src/chrome/browser/ui/browser_command_controller.cc?rcl=1470626560&l=383

...and the table that maps the accelerator key combo to IDC_MOVE_TAB_NEXT/PREVIOUS is here: https://cs.chromium.org/chromium/src/chrome/browser/ui/views/accelerator_table.cc?rcl=1470626560&l=77

For some reason, table entries only exist for Linux. So, let's add entries to make all of Windows/Mac/CrOS work the same; and add the Mac-standard ones for OS_MACOSX while we're at it.