Rename GDataFileSystem* to DriveFileSystem*

In this CL,
* gdata_file_system_interface.h has been renamed to drive_file_system_interface.{h,cc}
* gdata_file_system.{h,cc} have been renamed to drive_file_system.{h,cc}
* same for gdata_file_system_unittest.cc, gdata_file_system_proxy.{h,cc}, mock_gdata_file_system.{h,cc}
* class GDataFileSystemInterface has been renamed to DriveFileSystemInterface.
* class DriveFileSystem has been renamed to DriveFileSystem.

This change applies on top of
https://chromiumcodereview.appspot.com/10878023/

BUG=137151
TEST=pass all existing tests.
[email protected], [email protected], [email protected], [email protected]

Review URL: https://chromiumcodereview.appspot.com/10874028

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@153044 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/chromeos/gdata/drive_cache.h b/chrome/browser/chromeos/gdata/drive_cache.h
index 2b43e6e..735021b 100644
--- a/chrome/browser/chromeos/gdata/drive_cache.h
+++ b/chrome/browser/chromeos/gdata/drive_cache.h
@@ -65,7 +65,7 @@
 typedef base::Callback<void(bool success, const DriveCacheEntry& cache_entry)>
     GetCacheEntryCallback;
 
-// DriveCache is used to maintain cache states of GDataFileSystem.
+// DriveCache is used to maintain cache states of DriveFileSystem.
 //
 // All non-static public member functions, unless mentioned otherwise (see
 // GetCacheFilePath() for example), should be called from the sequenced
@@ -456,7 +456,7 @@
 };
 
 
-// The minimum free space to keep. GDataFileSystem::GetFileByPath() returns
+// The minimum free space to keep. DriveFileSystem::GetFileByPath() returns
 // GDATA_FILE_ERROR_NO_SPACE if the available space is smaller than
 // this value.
 //