gn2bp: add newlines in genrule commands for better diffs

Test: //base:base
Change-Id: I264d71709cd9e7d5ccc12e71252d1c01393687fe
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index 9ba1c80..476dbcf 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -667,6 +667,11 @@
 # There may be a better way to do target specific modification
 # Target specific modification before create_action_module
 def pre_create_action_module(target):
+  # Convert ['--param=value'] to ['--param', 'value'] for consistency.
+  # TODO: we may want to only do this for python scripts arguments. If argparse
+  # is used, this transformation is safe.
+  target.args = [str for it in target.args for str in it.split('=')]
+
   if target.script == "//build/write_buildflag_header.py":
     # write_buildflag_header.py writes result to args.genDir/args.output
     # So, override args.genDir by '.' so that args.output=$(out) works
@@ -694,12 +699,14 @@
     # Replace {{response_file_contents}} with /dev/stdin
     target.args = ['/dev/stdin' if it == response_file else it for it in target.args]
 
-  arg_string = ' '.join(target.args)
+  # put all args on a new line for better diffs.
+  NEWLINE = ' " +\n         "'
+  arg_string = NEWLINE.join(target.args)
   module.cmd = '$(location %s) %s' % (script, arg_string)
 
   if use_response_file:
     # Pipe response file contents into script
-    module.cmd = 'echo \'%s\' | %s' % (target.response_file_contents, module.cmd)
+    module.cmd = 'echo \'%s\' |%s%s' % (target.response_file_contents, NEWLINE, module.cmd)
 
   if all(os.path.splitext(it)[1] == '.h' for it in target.outputs):
     module.genrule_headers.add(bp_module_name)