[build] Do not fail build if source dir has 'debug' in it.

If the source checkout had 'debug' somewhere in the path name, then
IsDebuggerFile() marked all modules as debug ones, which triggered
an assertion during snapshot generation.

Bug: 
Change-Id: I93537efca9152c5469bb760f32ca53b06351f7a4
Reviewed-on: https://chromium-review.googlesource.com/809205Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49980}

AUTHORS

@@ -106,6 +106,7 @@ Michael Smith <mike@w3.org>
 Michaël Zasso <mic.besace@gmail.com>
 Mike Gilbert <floppymaster@gmail.com>
 Mike Pennisi <mike@mikepennisi.com>
+Mikhail Gusarov <dottedmag@dottedmag.net>
 Milton Chiang <milton.chiang@mediatek.com>
 Myeong-bo Shim <m0609.shim@samsung.com>
 Nicolas Antonius Ernst Leopold Maria Kaiser <nikai@nikai.net>

tools/js2c.py

@@ -365,7 +365,7 @@ class Sources:
 
 
 def IsDebuggerFile(filename):
-  return "debug" in filename
+  return os.path.basename(os.path.dirname(filename)) == "debug"
 
 def IsMacroFile(filename):
   return filename.endswith("macros.py")