lastchange: don't check git state for whether the tree is dirty
lastchange: don't check git state for whether the tree is dirty

We don't show whether the tree was dirty for SVN.

Because lastchange runs on every build, these commands impact every
build.  The call to "git checkout" makes git stat every file in the
repository (including ones unrelated to the build).

This change makes a Ninja build of Chrome 20% faster.  I've seen the
command take tens of seconds on a cold disk, and it likely has a
larger impact on Windows where the disk is slower.


Review URL: http://codereview.chromium.org/9148030

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@117352 0039d316-1c4b-4281-b951-d872f2087c98

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