Switch filetilestore over to using a proper LRU cache.

I plan on using the same LRU cache for merged tiles, but that will happen in a later CL.

BUG=skia:

Review URL: https://codereview.chromium.org/722833004
Fixed downloads in perf_setup.sh to writo to file

BUG=skia:3131
TBR=jcgregorio

Review URL: https://codereview.chromium.org/731503004
grcontexfactory moved to internal and broke fiddle

BUG=skia:

Review URL: https://codereview.chromium.org/740723002
build skgputest as part of setup for fiddle

BUG=skia:

Review URL: https://codereview.chromium.org/743683002
also build skflate during fiddle setup

BUG=skia:

Review URL: https://codereview.chromium.org/723943006
bug_chomper: Code restructurization.

Lets give it the same code structure we have been using at other places,
e.g.: perf/go/, golden/go/, monitoring/go.

And have the file that has the main package, named main.go.

BUG=None
R=borenet@google.com

Review URL: https://codereview.chromium.org/736583006