Fix error in timing tool when dragging outside the timeline track view
Fix error in timing tool when dragging outside the timeline track view

BUG=
R=dsinclair@chromium.org

Review URL: https://codereview.appspot.com/11840043
vmpstr/trace-viewer,SummerLW/Perf-Insight-Report,SummerLW/Perf-Insight-Report,vmpstr/trace-viewer,catapult-project/catapult,zeptonaut/catapult,sahiljain/catapult,dstockwell/catapult,danbeam/catapult,catapult-project/catapult,catapult-project/catapult,zeptonaut/catapult,dstockwell/catapult,catapult-project/catapult-csm,sahiljain/catapult,zeptonaut/catapult,SummerLW/Perf-Insight-Report,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult-csm,sahiljain/catapult,benschmaus/catapult,sahiljain/catapult,SummerLW/Perf-Insight-Report,sahiljain/catapult,SummerLW/Perf-Insight-Report,scottmcmaster/catapult,catapult-project/catapult-csm,dstockwell/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,vmpstr/trace-viewer,danbeam/catapult,0x90sled/catapult,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult-csm,catapult-project/catapult,danbeam/catapult,danbeam/catapult,0x90sled/catapult,modulexcite/catapult,modulexcite/catapult,catapult-project/catapult-csm,sahiljain/catapult,scottmcmaster/catapult,dstockwell/catapult,scottmcmaster/catapult,catapult-project/catapult,0x90sled/catapult,SummerLW/Perf-Insight-Report,benschmaus/catapult,benschmaus/catapult,modulexcite/catapult