Fix git cl format --diff --dry-run for Java files

A recent change added --diff support for Java files in git cl format,
but unfortunately it broke the behavior when both --dry-run and --diff
are passed, and made git cl format indicate that all changed files need
to be reformatted.

Fix so that --diff overrides --dry-run when running google-java-format,
as passing --dry-run makes the formatter only output file names which
then confused the diff creation code. This makes behavior for Java in
line with C++ where --dry-run doesn't change much if --diff is used.

Change-Id: I7f8eecb13064a0046935489e6c5cf3af566f7f56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5357818
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Tomasz Śniatowski <tomasz.sniatowski@xperi.com>

git_cl.py

@@ -6128,10 +6128,11 @@ def _RunGoogleJavaFormat(opts, paths, top_dir, upstream_commit):
         return 0
 
     base_cmd = [google_java_format, '--aosp']
-    if opts.dry_run:
-        base_cmd += ['--dry-run']
-    elif not opts.diff:
-        base_cmd += ['--replace']
+    if not opts.diff:
+        if opts.dry_run:
+            base_cmd += ['--dry-run']
+        else:
+            base_cmd += ['--replace']
 
     changed_lines_only = not (opts.full or settings.GetFormatFullByDefault())
     if changed_lines_only: