Revert of add gm to show miplevels (patchset #2 id:20001 of https://codereview.chromi...

Revert of add gm to show miplevels (patchset #2 id:20001 of https://codereview.chromium.org/849173004/)

Reason for revert:
==31530==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 224 byte(s) in 2 object(s) allocated from:
    #0 0x7febb223f65b in operator new(unsigned long) (/home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/dm+0x35865b)
    #1 0x7febb3483c56 in SkMipMap::Build(SkBitmap const&, SkDiscardableMemory* (*)(unsigned long)) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../src/core/SkMipMap.cpp:181:9
    #2 0x7febb2c37914 in ShowMipLevels::onDraw(SkCanvas*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../gm/downsamplebitmap.cpp:228:24
    #3 0x7febb2295736 in skiagm::GM::drawContent(SkCanvas*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../gm/gm.cpp:32:5
    #4 0x7febb2295019 in skiagm::GM::draw(SkCanvas*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../gm/gm.cpp:24:5
    #5 0x7febb226722f in DM::GMSrc::draw(SkCanvas*) const /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../dm/DMSrcSink.cpp:22:5
    #6 0x7febb226d929 in DM::RasterSink::draw(DM::Src const&, SkBitmap*, SkWStream*) const /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../dm/DMSrcSink.cpp:230:12
    #7 0x7febb224e004 in Task::Run(Task*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../dm/DM.cpp:254:25
    #8 0x7febb3805e4c in (anonymous namespace)::ThreadPool::Loop(void*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../src/core/SkTaskGroup.cpp:149:13
    #9 0x7febb460dc7c in thread_start(void*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../src/utils/SkThreadUtils_pthread.cpp:66:9
    #10 0x7febb1251f6d in start_thread /build/buildd/eglibc-2.17/nptl/pthread_create.c:311

Indirect leak of 699528 byte(s) in 2 object(s) allocated from:
    #0 0x7febb22214ab in __interceptor_malloc (/home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/dm+0x33a4ab)
    #1 0x7febb473e3c6 in sk_malloc_flags(unsigned long, unsigned int) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../src/ports/SkMemory_malloc.cpp:54:15
    #2 0x7febb473e19a in sk_malloc_throw(unsigned long) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../src/ports/SkMemory_malloc.cpp:40:12
    #3 0x7febb3483c94 in SkMipMap::Build(SkBitmap const&, SkDiscardableMemory* (*)(unsigned long)) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../src/core/SkMipMap.cpp:181:18
    #4 0x7febb2c37914 in ShowMipLevels::onDraw(SkCanvas*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../gm/downsamplebitmap.cpp:228:24
    #5 0x7febb2295736 in skiagm::GM::drawContent(SkCanvas*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../gm/gm.cpp:32:5
    #6 0x7febb2295019 in skiagm::GM::draw(SkCanvas*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../gm/gm.cpp:24:5
    #7 0x7febb226722f in DM::GMSrc::draw(SkCanvas*) const /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../dm/DMSrcSink.cpp:22:5
    #8 0x7febb226d929 in DM::RasterSink::draw(DM::Src const&, SkBitmap*, SkWStream*) const /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../dm/DMSrcSink.cpp:230:12
    #9 0x7febb224e004 in Task::Run(Task*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../dm/DM.cpp:254:25
    #10 0x7febb3805e4c in (anonymous namespace)::ThreadPool::Loop(void*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../src/core/SkTaskGroup.cpp:149:13
    #11 0x7febb460dc7c in thread_start(void*) /home/default/storage/skia-repo/buildbot/skiabot-linux-xsan-001/build/slave/Test-Ubuntu13_10-GCE-NoGPU-x86_64-Debug-ASAN/build/skia/out/Debug/../../src/utils/SkThreadUtils_pthread.cpp:66:9
    #12 0x7febb1251f6d in start_thread /build/buildd/eglibc-2.17/nptl/pthread_create.c:311

Original issue's description:
> add gm to show miplevels
>
> BUG=skia:
> TBR=
>
> NOTREECHECKS=true
>
> Committed: https://skia.googlesource.com/skia/+/a598f4b773f066a939e0216a116c179b90550727

TBR=reed@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/854103004