DevTools fails to find script for breakpoint

[elliette]

Dart DevTools is failing when I try to hit a breakpoint with the following error messaging in the console:

[SEVERE] Debugger: Failed to create dart frame for onClick: cannot find location for script 257
[WARNING] Debugger: Error calculating Dart frames
[SEVERE] Debugger: Failed to create dart frame for onClick: cannot find location for script 257
[WARNING] Debugger: Error calculating Dart frames
[SEVERE] Debugger: Failed to create dart frame for onClick: cannot find location for script 257
[WARNING] Debugger: Error calculating Dart frames
[SEVERE] Debugger: Failed to create dart frame for onClick: cannot find location for script 257
[WARNING] Debugger: Error calculating Dart frames
[SEVERE] Debugger: Failed to create dart frame for onClick: cannot find location for script 257
[WARNING] Debugger: Error calculating Dart frames

We recently changed how we are getting the script urls with #1559. It seems like there might be a few edge cases where we can't get the script. FYI @annagrin

[elliette]

Duplicate of #1581