Fix viewR computation in HighDPI
Fix viewR computation in HighDPI

Was not including the header with or the devicePixelRatio.

E.g. if the entire track view was 1000, and the header width was 150, and
devicePixelRatio was 2, then it was passing 1000 to the viewport.xViewToWorld.
Instead, it should be passing (1000 - 150) * 2.

BUG=304
R=dsinclair@chromium.org

Review URL: https://codereview.appspot.com/11210043
danbeam/catapult,sahiljain/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult,scottmcmaster/catapult,catapult-project/catapult-csm,dstockwell/catapult,catapult-project/catapult,modulexcite/catapult,dstockwell/catapult,vmpstr/trace-viewer,SummerLW/Perf-Insight-Report,modulexcite/catapult,catapult-project/catapult,danbeam/catapult,benschmaus/catapult,scottmcmaster/catapult,catapult-project/catapult,danbeam/catapult,vmpstr/trace-viewer,SummerLW/Perf-Insight-Report,scottmcmaster/catapult,sahiljain/catapult,modulexcite/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult,0x90sled/catapult,zeptonaut/catapult,catapult-project/catapult-csm,dstockwell/catapult,benschmaus/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult,sahiljain/catapult,benschmaus/catapult,catapult-project/catapult,danbeam/catapult,benschmaus/catapult,SummerLW/Perf-Insight-Report,zeptonaut/catapult,zeptonaut/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,benschmaus/catapult,vmpstr/trace-viewer,benschmaus/catapult,catapult-project/catapult-csm,0x90sled/catapult,sahiljain/catapult,sahiljain/catapult,dstockwell/catapult,0x90sled/catapult,benschmaus/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,sahiljain/catapult