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To optimize the font family search, mRanges is used for narrowing down the search range. However, mRanges is constructed from format 4 or format 12 entries. So, if the font supports a variation sequence but doesn't support the base character of the sequence, the font may not be listed in mRanges. The proper way to fix this issue is using format 14 subtable information for mRanges construction. However, this is not a trivial work since currently we rely on HarfBuzz for variation sequence lookup and it doesn't provide any API for retrieving coverage information. Thus, as the quick fix, iterate all font families in font fallback chain if the variation sequence is specified. Change-Id: I278da84be8fb8f553590e2e42ed450b7e4a34eca