Add protobuf serialization to DisplayItemList

Serialize the following classes:
- DisplayItemListSettings
- DisplayItemList
- DisplayItem and all subclasses
  - Did not fully serialize FilterDisplayItem.  Serializing
    FilterOperations will require more work.  Will do in a follow up CL.

Added unit tests for all DisplayItems serialized.

BUG=541321
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1407793002

Cr-Commit-Position: refs/heads/master@{#356563}

• cc/BUILD.gn[diff]
• cc/cc.gyp[diff]
• cc/playback/clip_display_item.cc[diff]
• cc/playback/clip_display_item.h[diff]
• cc/playback/clip_path_display_item.cc[diff]
• cc/playback/clip_path_display_item.h[diff]
• cc/playback/compositing_display_item.cc[diff]
• cc/playback/compositing_display_item.h[diff]
• cc/playback/display_item.h[diff]
• cc/playback/display_item_list.cc[diff]
• cc/playback/display_item_list.h[diff]
• cc/playback/display_item_list_settings.cc[diff]
• cc/playback/display_item_list_settings.h[diff]
• cc/playback/display_item_list_unittest.cc[diff]
• cc/playback/display_item_proto_factory.cc[Added - diff]
• cc/playback/display_item_proto_factory.h[Added - diff]
• cc/playback/drawing_display_item.cc[diff]
• cc/playback/drawing_display_item.h[diff]
• cc/playback/filter_display_item.cc[diff]
• cc/playback/filter_display_item.h[diff]
• cc/playback/float_clip_display_item.cc[diff]
• cc/playback/float_clip_display_item.h[diff]
• cc/playback/transform_display_item.cc[diff]
• cc/playback/transform_display_item.h[diff]
• cc/proto/BUILD.gn[diff]
• cc/proto/display_item.proto[Added - diff]
• cc/proto/gfx_conversions.h[diff]
• cc/proto/skia_conversions.h[diff]