Implement more font stuff.

* glyph bounding boxes
* testing wether a font can print a given string
DumpRenderTree: dump frames.
Implement waiting for tests to terminate.

Instead of dumping test results immediately after loading, some tests
require DumpRenderTree to wait and notify it whe nthey are done. Add
support for this in our version of DumpRenderTree.

This makes the testsuite take a lot more time to run through, however
(in the range of hours). A lot of tests are timing out currently. Our
options are making them work, skip them, or make the timeouts much
smaller to get things going reasonably fast - at the risk of some tests
timing out where they could succeed. The testsuite script have a notion
of "slow" tests, for which a longer timeout is used. Marking tests as
slow ads even more work to that testsuite thing, however.
Fix localized string.

This one is hardcoded in testsuite results, so let's use the expected
one.
Implement topLoadingFrame support in DRT.

Without this, some tests dumped results twice, with the first dump
possibly before things were done running.