Use variable length key (rather than accumulated matrix) as save layer hoisting key
Adding the rendering canvas' CTM to the layer hoisting key (i.e., Add support for hoisting layers in pictures drawn with a matrix - https://codereview.chromium.org/748853002/) has increased the cache miss rate due to accumulated floating point error. This CL fixes part of the issue by using the chain of operation indices leading to each saveLayer as the key. The canvas' CTM must still form part of the key but should be less subject to accumulated error.
BUG=skia:2315
Review URL: https://codereview.chromium.org/753253002
14 files changed