Fixed icon_util_unittest writing files to checkout directory.

Fixed icon_util_unittest writing files to checkout directory.

- Does not create or attempt to create files in .\ui\gfx\test\data or C:\. Uses
  the scoped temporary directory instead.
- Calls CreateUniqueTempDir so that the scoped temporary directory is actually a
  temporary directory, and not the current working directory.

Also made other miscellaneous fixes:

- Consistently uses "temp_test_icon.ico" instead of "test.ico".
- Tests that CreateIconFileFromSkBitmap with invalid parameters actually does
  not create the file (instead of trusting its return value).
- Initializes test class using SetUp instead of constructor.
- Fixed spelling of "dimensions".

BUG=118246

Review URL: https://chromiumcodereview.appspot.com/14148005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@194806 0039d316-1c4b-4281-b951-d872f2087c98