Bug 1262978: Run npm to get the path to installed binaries if eslint can't otherwise be found. r=gps

MozReview-Commit-ID: HFWID6QhpS2

--HG--
extra : rebase_source : bed90ecf7b59b348ec5047c9ac9e8cc31a2aa193
extra : amend_source : 97f81e0bb34098c1aaad1b2ad4355d3f0ad6f72c

python/mach_commands.py

@@ -166,7 +166,18 @@ class MachCommands(MachCommandBase):
                 try:
                     binary = which.which('eslint')
                 except which.WhichError:
-                    pass
+                    npmPath = self.getNodeOrNpmPath("npm")
+                    if npmPath:
+                        try:
+                            output = subprocess.check_output([npmPath, "bin", "-g"],
+                                                             stderr=subprocess.STDOUT)
+                            if minversion:
+                                base = output.split("\n").strip()
+                                binary = os.path.join(base, "eslint")
+                                if not os.path.is_file(binary):
+                                    binary = None
+                        except (subprocess.CalledProcessError, WindowsError):
+                            pass
 
         if not binary:
             print(ESLINT_NOT_FOUND_MESSAGE)