Add placeholder git hooks.
Add placeholder git hooks.

This is a bit of future-proofing.  The git hooks in depot_tools/git-templates/hooks all try to forward to build/git-hooks.

Currently, the only actual hook we have is in src/build/git-hooks/pre-commit, which (usefully) makes sure no one inadvertently commits a submodule change.  If we want to add more git hooks, we can simply commit them to build/git-hooks, rather than asking everyone to modify .git/hooks in their checkout.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/14230012

git-svn-id: fd409f4bdeea2bb50a5d34bb4d4bfc2046a5a3dd@195336 0039d316-1c4b-4281-b951-d872f2087c98

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