9769 Document //flutter/shell/common/engine.

9772 fix objcdoc generation

9781 SendPlatformMessage allow null message value

9797 Remove breaking asserts

9808 Document FontFeature class

9809 Document //flutter/shell/common/rasterizer

9813 Made Picture::toImage happen on the IO thread with no need for an onscreen surface.

9815 Made the persistent cache’s directory a const pointer.

9816 Only release the image data in the unit-test once Skia has accepted ownership of it.

9825 In a single frame codec, release the encoded image buffer after giving it to the decoder

9828 Make the virtual display’s window translucent

9847 Started adding the engine hash to frameworks’ Info.plist.