UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 YaBrowser/16.6.0.8125 Safari/537.36

Steps to reproduce the problem:
1. Create extension with 'debugger' permission
2. Open tab (e.g. google.com) and open devtools on it
3. From background page call `chrome.debugger.getTargets()`
Ensure that tab with google has {attached: true} property.
4. Try send some debugger command, e.g.:
chrome.debugger.sendCommand({tabId: <tab-id>}, 'Network.enable', {}, res => console.log(res))

What is the expected behavior?
Debugger TargetInfo should contain some flag that attached debugger is devtools and actually it is impossible to send any command to it (or even re-attach new debugger instead of devtools' one)

For example:
{
  attached: true,
  isDevtools: true
  // or
  debuggerType: 'devtools'
  ...
}

What went wrong?
Impossible to differentiate devtools debugger from external debugger.
That causes inconsistency:
getTargets() returns 'attached': true, but actually I cant send any debugger command.
The error message is:
"Debugger is not attached to the tab with id: ..."

WebStore page: 

Did this work before? No 

Chrome version: 50.0.2661.102  Channel: stable
OS Version: OS X 10.11.5
Flash Version: Shockwave Flash 22.0 r0

This makes sense until this issue will be resolved: https://bugs.chromium.org/p/chromium/issues/detail?id=403324