WebView performance regression in 8u60

Test code is available from https://github.com/larc63/WebView-Performance

As noted in the github repo, performance reduced by 2.3x between 8u51 and 8u60:

Update Time (ms)
1.8.0_40 1771
1.8.0_45 1693
1.8.0_51 1716
1.8.0_60 3969
1.8.0_65 3958
1.8.0_66 4059
1.8.0_74 3862
1.8.0_92 4008