gdata: Move GDataCache::CacheEntry out of GDataCache

Along the way, rename it to GDataCacheEntry to be consistent
with other classes, and put it in a separate header file.

FWIW, nested classes are usually avoided.
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Nested_Classes

BUG=136625
TEST=out/Release/unit_tests --gtest_filter=GData*

Review URL: https://chromiumcodereview.appspot.com/10690149

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@146236 0039d316-1c4b-4281-b951-d872f2087c98
17 files changed