components: Add components_strings target to GN build.

I need this for bookmarks component, which will come next.

BUG=None
TEST=gn gen out/Debug_gn && ninja -C out/Debug_gn components_strings
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Review URL: https://codereview.chromium.org/361623002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@280763 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed