YCM works correctly when 'out' directory is a symlink (continued).

It used to work after my previous fix 37accc2c, but then it broke again.
This CL changes the way how "-I" arguments are transformed.

BUG=NONE
TEST=manually
NOTRY=true

Review URL: https://codereview.chromium.org/528293002

Cr-Commit-Position: refs/heads/master@{#293519}

tools/vim/chromium.ycm_extra_conf.py

@@ -166,12 +166,11 @@ def GetClangCommandFromNinjaForFilename(chrome_root, filename):
         # try to use the default flags.
         return chrome_flags
 
-  out_dir = GetNinjaOutputDirectory(chrome_root)
+  out_dir = os.path.realpath(GetNinjaOutputDirectory(chrome_root))
 
   # Ninja needs the path to the source file relative to the output build
   # directory.
-  rel_filename = os.path.relpath(os.path.realpath(filename),
-                                 os.path.realpath(out_dir))
+  rel_filename = os.path.relpath(os.path.realpath(filename), out_dir)
 
   # Ask ninja how it would build our source file.
   p = subprocess.Popen(['ninja', '-v', '-C', out_dir, '-t',