Count app dirty pages against zygote in imgdiag

Modify ComputeDirtyBytes to compare app and zygote pages
Remove dirty page counting from ImgDiagDumper::Init

imgdiag output before:
 Mapping at [0x6f3c2000, 0x6f658000) had:
   860164 differing bytes,
   286718 differing int32s,
   662 differing pages,
   662 pages are dirty;
   0 pages are false dirty;
   55 pages are private;
   55 pages are Private_Dirty

After:
 Mapping at [0x6f3c2000, 0x6f658000) had:
   848 differing bytes,
   256 differing int32s,
   48 differing pages,
   55 pages are dirty;
   7 pages are false dirty;
   55 pages are private;
   55 pages are Private_Dirty

Test: m imgdiag
Change-Id: I99ccf2ab91068d63fb28b03a6d5732879b80431e
1 file changed