prepareMailbox 376 Source/platform/graphics/Canvas2DLayerBridge.cpp bool Canvas2DLayerBridge::prepareMailbox(blink::WebExternalTextureMailbox* outMailbox, blink::WebExternalBitmap* bitmap) prepareMailbox 163 Source/platform/graphics/gpu/DrawingBuffer.cpp bool DrawingBuffer::prepareMailbox(blink::WebExternalTextureMailbox* outMailbox, blink::WebExternalBitmap* bitmap)