[Android] memory_inspector: bug / UI fixes.

This is a set of bug / UI fixes for memory inspector, in preparetion
for next CLs which will introduce integration with libheap_profiler.
Changes in this CL:
- Introduce mmap de-offset heplers (will be used soon for intersecting
  native heap traces).
- Fix symbol lookup for shared_library Chrome builds.
- Add RSS column to mmaps table.
- Add server crash / unreachable detection.
- Update prebuilts (add also desktop ones for paul.whitton@)
- Make it possible to filter tests ran by run_tests.
- Minor cosmetic bugfixes.

BUG=340294

Review URL: https://codereview.chromium.org/559023002

Cr-Commit-Position: refs/heads/master@{#294193}

• tools/memory_inspector/memory_inspector/backends/android/android_backend.py[diff]
• tools/memory_inspector/memory_inspector/backends/android/dumpheap_native_parser.py[diff]
• tools/memory_inspector/memory_inspector/backends/prebuilts_fetcher.py[diff]
• tools/memory_inspector/memory_inspector/constants.py[diff]
• tools/memory_inspector/memory_inspector/core/memory_map.py[diff]
• tools/memory_inspector/memory_inspector/core/memory_map_unittest.py[diff]
• tools/memory_inspector/memory_inspector/core/native_heap.py[diff]
• tools/memory_inspector/memory_inspector/core/stacktrace.py[diff]
• tools/memory_inspector/memory_inspector/frontends/background_tasks.py[diff]
• tools/memory_inspector/memory_inspector/frontends/www_content/css/rootUi.css[diff]
• tools/memory_inspector/memory_inspector/frontends/www_content/js/devices.js[diff]
• tools/memory_inspector/memory_inspector/frontends/www_content/js/mmap.js[diff]
• tools/memory_inspector/memory_inspector/frontends/www_content/js/processes.js[diff]
• tools/memory_inspector/memory_inspector/frontends/www_content/js/rootUi.js[diff]
• tools/memory_inspector/memory_inspector/frontends/www_content/js/webservice.js[diff]
• tools/memory_inspector/memory_inspector/frontends/www_server.py[diff]
• tools/memory_inspector/prebuilts/memdump-android-arm.sha1[diff]
• tools/memory_inspector/prebuilts/memdump-linux-x86_64.sha1[diff]
• tools/memory_inspector/prebuilts/ps_ext-android-arm.sha1[diff]
• tools/memory_inspector/prebuilts/ps_ext-linux-x86_64.sha1[Added - diff]
• tools/memory_inspector/run_tests[diff]