Malloc debug rewrite.

The major components of the rewrite:

- Completely remove the qemu shared library code. Nobody was using it
  and it appears to have broken at some point.
- Adds the ability to enable/disable different options independently.
- Adds a new option that can enable the backtrace on alloc/free when
  a process gets a specific signal.
- Adds a new way to enable malloc debug. If a special property is
  set, and the process has an environment variable set, then debug
  malloc will be enabled. This allows something that might be
  a derivative of app_process to be started with an environment variable
  being enabled.
- get_malloc_leak_info() used to return one element for each pointer that
  had the exact same backtrace. The new version returns information for
  every one of the pointers with same backtrace. It turns out ddms already
  automatically coalesces these, so the old method simply hid the fact
  that there where multiple pointers with the same amount of backtrace.
- Moved all of the malloc debug specific code into the library.
  Nothing related to the malloc debug data structures remains in libc.
- Removed the calls to the debug malloc cleanup routine. Instead, I
  added an atexit call with the debug malloc cleanup routine. This gets
  around most problems related to the timing of doing the cleanup.

The new properties and environment variables:

libc.debug.malloc.options
  Set by option name (such as "backtrace"). Setting this to a bad value
  will cause a usage statement to be printed to the log.

libc.debug.malloc.program
  Same as before. If this is set, then only the program named will
  be launched with malloc debug enabled. This is not a complete match,
  but if any part of the property is in the program name, malloc debug is
  enabled.

libc.debug.malloc.env_enabled
  If set, then malloc debug is only enabled if the running process has the
  environment variable LIBC_DEBUG_MALLOC_ENABLE set.

Bug: 19145921

Change-Id: I7b0e58cc85cc6d4118173fe1f8627a391b64c0d7
diff --git a/README.md b/README.md
index 6739926..c6b9278 100644
--- a/README.md
+++ b/README.md
@@ -118,6 +118,10 @@
     # current upstream source in one of the upstream directories or by
     # switching the file to C++ and cleaning it up.
 
+  malloc_debug/
+    # The code that implements the functionality to enable debugging of
+    # native allocation problems.
+
   stdio/
     # These are legacy files of dubious provenance. We're working to clean
     # this mess up, and this directory should disappear.