Subzero: Fix build problem against LLVM trunk. LLVM commit 4ac35e82723d4bdbc094f73b2d33aaaa86a00d6a removed some code that Subzero still needs, specifically StreamingMemoryObject and its parents. Deal with this by adding those files back to the Subzero repo. This allows Subzero to build through LLVM c75e3c2fd2bb9ca010f4e1c32acbd142adc32c7f. BUG= none [email protected] Review-Url: https://codereview.chromium.org/2605653002 .