Bug: 31781480
Test: manual
The cache is useful when setting summary text on tiles. If tile cache is
cleared and rebuilt, summaryloader won't find existing tile to update
summary.
The cache should only be cleared when entire resource config changes,
tracked by InterestingConfigChnages.
Change-Id: I3afcaba30b835f59ffaad9c27564f0345af00d66
5adc26695f