This patch implements FrameManager which is responsible for maintaining
the frame tree. FrameManager is quite basic: it sends FrameAttached,
FrameDetached and FrameNavigated events, and can report mainFrame and
all frames.
The next step would be moving certain Page API's to the Frame. For
example, such method as Page.evaluate, Page.navigate and others should
be available on Frame object as well.
References #4
This patch introduces a goldentest.js. The tests inside
the file should rely on "golden" results rather then asserts.
For now, goldentest.js allows only image expectations. If the
actual result doesn't match the expected result, the two files
are created under `test/output` folder:
- The '-actual.png' contains the actual test result
- The '-diff.png' contains the diff between images
