DevTools: [CodeMirror] fix indentation bug
DevTools: [CodeMirror] fix indentation bug

Fix indentation bug in CodeMirrorTextEditor. The bug
was caused by the fact that "function foo() {".substr(0 - 1, 1) returns
"{".

BUG=256231

Review URL: https://chromiumcodereview.appspot.com/18332006

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@153350 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs