Fix Python imported modules depfile generation
Some Python scripts incorrectly reported no python module deps, for
example a manual run of build/android/gn/zip.py would create an empty
depfile (without even a build_utils.py entry).
GetPythonDependencies assumed that CHROMIUM_SRC is an absolute path,
turns out that depends on details of how build_utils.py is imported.
If it happened to be relative, all modules would be omitted from the
depfile as "system" modules, as they did not match CHROMIUM_SRC. Fix by
using DIR_SOURCE_ROOT which is absolute (and assert that it is).
R=cjhopman@chromium.org, agrieve@chromium.org
BUG=359249
Review URL: https://codereview.chromium.org/1412793012
Cr-Commit-Position: refs/heads/master@{#357246}
2 files changed
