Reset currentBarMouseOverTarget_ on picture change
Reset currentBarMouseOverTarget_ on picture change

Not resetting it causes exceptions when changing picture if
currentBarMouseOverTarget_ >= the pictureOps_.length.

R=nduca@chromium.org

Review URL: https://codereview.appspot.com/94080043
benschmaus/catapult,SummerLW/Perf-Insight-Report,0x90sled/catapult,SummerLW/Perf-Insight-Report,sahiljain/catapult,catapult-project/catapult,0x90sled/catapult,scottmcmaster/catapult,sahiljain/catapult,sahiljain/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult,sahiljain/catapult,SummerLW/Perf-Insight-Report,modulexcite/catapult,vmpstr/trace-viewer,dstockwell/catapult,modulexcite/catapult,catapult-project/catapult,zeptonaut/catapult,sahiljain/catapult,catapult-project/catapult,danbeam/catapult,benschmaus/catapult,benschmaus/catapult,dstockwell/catapult,dstockwell/catapult,danbeam/catapult,scottmcmaster/catapult,catapult-project/catapult-csm,zeptonaut/catapult,modulexcite/catapult,danbeam/catapult,catapult-project/catapult-csm,danbeam/catapult,benschmaus/catapult,sahiljain/catapult,catapult-project/catapult-csm,vmpstr/trace-viewer,SummerLW/Perf-Insight-Report,dstockwell/catapult,catapult-project/catapult,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult-csm,zeptonaut/catapult,catapult-project/catapult,0x90sled/catapult,vmpstr/trace-viewer,catapult-project/catapult-csm,scottmcmaster/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult-csm,SummerLW/Perf-Insight-Report,benschmaus/catapult