HostConnection: Use unique_ptr in HostConnection class members.

Fuchsia LeakSanitizer has found a memory leak in
goldfish ICD due to not deleting "m_vkEnc" in dtor
of HostConnection. Using smart pointers instead of
"new" and "delete" will help us prevent bugs like

This change removes most new/delete usages within
HostConnection, and use std::unique_ptr instead.

TEST=fuchsia escher_tests, scenic_tests with LSan turned on.

Change-Id: I42b46ee4a25c872e7eb493bf55228f9e017b5887
3 files changed