Verify that breakpoints are moved appropriately


Running: addFileSystem

Running: setBreakpointInFileSystemUISourceCode
    file:///var/www/devtools/persistence/resources/foo.js:2

Running: addFileMapping
    http://127.0.0.1:8000/devtools/persistence/resources/foo.js:2

Running: removeFileMapping
    file:///var/www/devtools/persistence/resources/foo.js:2
    http://127.0.0.1:8000/devtools/persistence/resources/foo.js:2