Remove unused forward declaration
Remove unused forward declaration

class Task is not used in main_function_params.h

BUG=none
TEST=compile

Review URL: http://codereview.chromium.org/9956074

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@131258 0039d316-1c4b-4281-b951-d872f2087c98

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