[esan|cfrag] Add counters for struct array accesses

Summary:
Adds one counter to the struct counter array for counting struct
array accesses.

Adds instrumentation to insert counter update for struct array
accesses.

Reviewers: aizatsky

Subscribers: llvm-commits, bruening, eugenis, kcc, zhaoqin, vitalybuka

Differential Revision: http://reviews.llvm.org/D21594

llvm-svn: 274420