https://bugs.webkit.org/show_bug.cgi?id=28751

Reviewed by Adam Barth.

* Make code mostly comply with the style guide (switch indenting, use of
  "!" vs. "== 0", don't unnecessarily wrap lines, etc.)
* Eliminate m_allDataReceived in ICO/BMP decoders since it's in the
  base ImageDecoder class
* Remove some useless or wrong comments, add others
* Wrap comments at 80 columns (most already were) for
  consistency/readability
* Avoid casts by using correct variable types
* Consistent naming of decode() function/args
* Shorter code in some places
* Make declaration and definition order match

* platform/graphics/qt/ImageDecoderQt.cpp:
(WebCore::ImageDecoderQt::frameCount):
(WebCore::ImageDecoderQt::frameBufferAtIndex):
(WebCore::ImageDecoderQt::forceLoadEverything):
* platform/image-decoders/ImageDecoder.cpp:
(WebCore::ImageDecoder::create):
(WebCore::RGBA32Buffer::clear):
(WebCore::RGBA32Buffer::setSize):
* platform/image-decoders/ImageDecoder.h:
(WebCore::...