content/renderer: depend on v8 explicitly
content/renderer: depend on v8 explicitly

Files like render_thread use v8:: functions, so make the v8
dependency explicit.  This is needed for the multi-dll net build.

Review URL: http://codereview.chromium.org/7301020

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@92057 0039d316-1c4b-4281-b951-d872f2087c98

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