Instead of a list of strings given by their length and UTF-8 encoding,
restructure the string table to consist of a list of string ending
offsets followed by a blob of UTF-8 encoded strings without lengths.
This is a step toward copying the string blob into the VM's heap and
building a heap-allocated structure to give random access to them.
BUG=
R=asgerf@google.com, jensj@google.com
Review-Url: https://codereview.chromium.org/2790073004 .