add test cases including: filled & stroked arc, image, line with different caps, join and stroke operations, compositing operations, text and transformation.
Originally we measure the time difference between script load
and body onload message, but we cannot guarantee the updated frame are
painted before the onload message. So the measure results are almost
meanless. This is also the reason we get benchmark result with large
variance.

Now we update the frame for several times, and measure the time difference
between script load time and the last frame's animation event.
add a test case to show font rendering performance
Added a test launcher for misc layout like tests.