add Utils object to provides functions required by Canvas2D tests.
add missing <html> tag.
add Canvas2D case :
  draw convex quadratic bezier curves
  draw concave quadratic bezier curves
  draw rectangle with gradient fill style
  draw rectangle with shadow
  draw patterned rectangle
  draw image
  image data
    this case mainly measure the performance of accessing pixel data, not get/put image data

enable newly added test cases.
  replace new Array() with [] to create array object, so that we can even add comma at the last cases. This will be convenient for us to debug test cases.

add loadImg() and getRandomColor() to Utils object which are commonly used by several test cases.