Use the viewport device pixel ratio instead of the raw device pixel ratio.
Use the viewport device pixel ratio instead of the raw device pixel ratio.

This fixes unit test failures on lowDPI machines.
catapult-project/catapult,vmpstr/trace-viewer,benschmaus/catapult,catapult-project/catapult,modulexcite/catapult,catapult-project/catapult,zeptonaut/catapult,dstockwell/catapult,0x90sled/catapult,sahiljain/catapult,catapult-project/catapult,modulexcite/catapult,scottmcmaster/catapult,sahiljain/catapult,catapult-project/catapult-csm,SummerLW/Perf-Insight-Report,zeptonaut/catapult,SummerLW/Perf-Insight-Report,modulexcite/catapult,SummerLW/Perf-Insight-Report,dstockwell/catapult,benschmaus/catapult,catapult-project/catapult-csm,SummerLW/Perf-Insight-Report,benschmaus/catapult,SummerLW/Perf-Insight-Report,sahiljain/catapult,scottmcmaster/catapult,catapult-project/catapult-csm,danbeam/catapult,sahiljain/catapult,sahiljain/catapult,0x90sled/catapult,dstockwell/catapult,danbeam/catapult,danbeam/catapult,catapult-project/catapult,dstockwell/catapult,vmpstr/trace-viewer,SummerLW/Perf-Insight-Report,vmpstr/trace-viewer,catapult-project/catapult,benschmaus/catapult,catapult-project/catapult-csm,sahiljain/catapult,benschmaus/catapult,danbeam/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult-csm,zeptonaut/catapult,benschmaus/catapult,catapult-project/catapult,0x90sled/catapult,scottmcmaster/catapult,benschmaus/catapult