Version: Top of tree
OS: Mac OS X 10.11

What steps will reproduce the problem?
(1) gn args out/Default
(2) set is_component_build = true
(3) Wait for gn to try to generate Ninja files

What is the expected output?

Meaningful assertion message at the correct line number

What do you see instead?

[mfoltz@mfoltz-macpro /Users/mfoltz/chrome/src]$ gn args out/Default
Waiting for editor on "/Users/mfoltz/chrome/src/out/Default/args.gn"...
Waiting for Emacs...
Generating files...
ERROR at //chrome/BUILD.gn:254:5: Assertion failed.
    assert(false)
    ^-----

Please use labels and text to provide additional information.


NOTE:
There is no assertion message, or assertion statement at line 254 of chrome/BUILD.gn, so it's not easy to tell what config caused this problem.  Manual bisecting of args.gn points to "is_component_build" as the culprit.