Several changes as per Russ and Ian requests:
1. Fix almost broken ZoomIn/ZoomOut/Newer/Older with ability zoom in/out and move left/right w/o reloading (the 'explorer' attribute on graph).
2. Start the graph from the current release by default.
3. Allow to select the range of commits by specifying release range (e.g. go1.1 to go1.3 or go1.3 to tip).
4. Make it visually clear that you can select several benchmarks/metrics (replace select with a set of checkboxes).
5. Remove the "absolute" mode. Instead normalize all metrics to the start of the release (start becomes 1.0) and all subsequent changes are relative to it.
LGTM=adg
R=adg
CC=golang-codereviews, iant, rsc
https://golang.org/cl/159980043
This CL moves code from code.google.com/p/dvyukov-go-perf-dashboard,
which was previously reviewed.
LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/96180043
Dmitriy Vyukov