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.

git-svn-id: 3a56fcae908c7e16d23cb53443ea4795ac387cf2@579 0e6d7f2b-9903-5b78-7403-59d27f066143

bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer