Summary: Pad and cache-align BiasedMappedArray instances by default to avoid performance variability problems due to false sharing, as instances of this data structures are typically used for performance sensitive code.
Reviewed-by: brutisso, stefank

Summary: Add G1BiasedArray<T> that is an array where each element represents a fixed-sized subdivision of the heap. Use this abstraction to refactor the HeapRegionSeq class.
Reviewed-by: brutisso