[asan] asan_allocator2: improve FindHeapChunkByAddress to find memory chunks to the left of a given address. Almost all tests pass with the new allocator now, only 6 are left to fix.

llvm-svn: 170511

llvm-svn: 170339

llvm-svn: 170329

llvm-svn: 170315

llvm-svn: 170310

llvm-svn: 170193

llvm-svn: 170190

llvm-svn: 169985

llvm-svn: 169864

llvm-svn: 169836

[asan] introduce asan_allocator2.cc, which will have the replacement for asan allocator (now, just a bit of boilerplate)

llvm-svn: 169733