Add methods for cache_temperature: ClearCache, WarmCache (refactoring of cache_temperature)
Add methods for cache_temperature: ClearCache, WarmCache
(refactoring of cache_temperature)

This CL refactors cache_temperature in order to add new
cache_temperature state 'HOT' in the following CL:
https://codereview.chromium.org/3011263002/

BUG=chromium:736697

Review-Url: https://chromiumcodereview.appspot.com/3013213002

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