Don't delete .manifest files generated by gyp when doing clobber
Don't delete .manifest files generated by gyp when doing clobber

gyp windows ninja generates manifest files at generation time
but clobber nukes at the beginning of compile, so make sure
not to delete those generated files, otherwise compile will fail.

BUG=331082

Review URL: https://codereview.chromium.org/125133007

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@243182 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build