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Previously, layer titles found their way into the resource manager
as ANDROID_RESOURCE_TYPE_DYNAMIC_BITMAP and were left there forever.
Over time, these recources accumulated (easily reproducable by
entering and exiting the tab switcher) and is more than likely the
cause of memory related crashes when entering the tab switcher.
The title layer itself was removed from the LayerTitleCache but the
resources that constitute the title were never correctly managed.

This change adds a function to the ResourceManager that allows the
LayerTitleCache to remove associated resources. Specifically, only
dynamic bitmaps can be manually removed.

BUG=669348

Review-Url: https://codereview.chromium.org/2578233002
Cr-Commit-Position: refs/heads/master@{#441773}