SkPDF: Implement drawImage*() properly

drawImage calls now properly embeds the original jpeg.

NOTE: drawBitmap*() calls no longer embed JPEG files when
possible (this is in advance of eliminating bitmaps backed
by encoded data).  Chromium has already moved from
drawBitmap to drawImage.

Comparisons:

control:
    total PDF drawImage/drawBitmap calls: 8010
    total PDF jpeg images: 0
    total PDF regular images: 3581

experiament:
    total PDF drawImage/drawBitmap calls: 8014
    total PDF jpeg images: 271
    total PDF regular images: 3311
    total PDF regular images: 3582 (271 + 3311)

When comparing rendered output there were perceptual
differences in the following four GMs: colorcube, emboss,
colormatrix, and tablecolorfilter.  All of these differences
were improvements (that is, closer to the 8888 rendering)
due fixing a bug with colorfilters and forgetting to call
notifyPixelsChanged.

No SKPs had perceptual differences.

Total PDF size dropped from 133964 kB to 126276 kB, a 5.7%
improvement (mostly due to restoring use of JPG images in
SKPs).

BUG=skia:4370

Review URL: https://codereview.chromium.org/1372783003
14 files changed