Allow PNG_EASY_ACCESS_SUPPORTED

Allow PNG_EASY_ACCESS_SUPPORTED by not defining PNG_NO_EASY_ACCESS. This
enables [wk_]png_get_image_width, [wk_]png_get_image_height, and
[wk_]png_get_interlace_type, required for
https://bugs.webkit.org/show_bug.cgi?id=54406.

This is needed to allow WebKit to build with libpng 1.5, which no longer allows
direct access to the underlying struct members without using the "easy access"
accessors.

BUG=webkit:54406
TEST=That patch can land without breaking Chromium
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=79710

[Mark Mentovai, 2011-03-29 16:16:43]

thakis and agl, because you’re the last two guys to have made real changes in
libpng.

[agl, 2011-03-29 16:19:13]

LGTM

[Nico, 2011-03-30 15:21:47]

LG

[Nico, 2011-03-30 15:35:56]

Code archeologists: see
http://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thre...