Fix view always centering when navigating to a single Instant
Fix view always centering when navigating to a single Instant

This change fixes that the screen gets always centered on an Instant slice
when navigating to it while searching or using arrow keys. Now the view
only centers on the Instant in case it is offscreen.

BUG=
R=dsinclair@chromium.org

Review URL: https://codereview.appspot.com/11215043
0x90sled/catapult,catapult-project/catapult,benschmaus/catapult,modulexcite/catapult,catapult-project/catapult-csm,dstockwell/catapult,scottmcmaster/catapult,catapult-project/catapult,catapult-project/catapult-csm,SummerLW/Perf-Insight-Report,sahiljain/catapult,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult,sahiljain/catapult,benschmaus/catapult,dstockwell/catapult,danbeam/catapult,modulexcite/catapult,sahiljain/catapult,catapult-project/catapult,dstockwell/catapult,danbeam/catapult,catapult-project/catapult-csm,dstockwell/catapult,SummerLW/Perf-Insight-Report,benschmaus/catapult,catapult-project/catapult-csm,zeptonaut/catapult,zeptonaut/catapult,catapult-project/catapult-csm,SummerLW/Perf-Insight-Report,sahiljain/catapult,SummerLW/Perf-Insight-Report,danbeam/catapult,sahiljain/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,modulexcite/catapult,benschmaus/catapult,scottmcmaster/catapult,zeptonaut/catapult,SummerLW/Perf-Insight-Report,sahiljain/catapult,vmpstr/trace-viewer,catapult-project/catapult,benschmaus/catapult,scottmcmaster/catapult,SummerLW/Perf-Insight-Report,0x90sled/catapult,vmpstr/trace-viewer,0x90sled/catapult,vmpstr/trace-viewer,catapult-project/catapult,catapult-project/catapult,danbeam/catapult