Added support for creating a SKCanvas from a SKBitmap

binding/Binding/SKCanvas.cs

@@ -19,6 +19,14 @@ namespace SkiaSharp
 		{
 		}
 
+		public SKCanvas (SKBitmap bitmap)
+			: this (IntPtr.Zero, true)
+		{
+			if (bitmap == null)
+				throw new ArgumentNullException (nameof (bitmap));
+			Handle = SkiaApi.sk_canvas_new_from_bitmap (bitmap.Handle);
+		}
+
 		public int Save ()
 		{
 			if (Handle == IntPtr.Zero)

binding/Binding/SkiaApi.cs

@@ -175,6 +175,8 @@ namespace SkiaSharp
 		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]
 		[return: MarshalAs(UnmanagedType.I1)]
 		public extern static bool sk_canvas_get_clip_bounds(sk_canvas_t t, ref SKRect cbounds);
+		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]
+		public extern static sk_canvas_t sk_canvas_new_from_bitmap(sk_bitmap_t bitmap);
 
 		[DllImport(SKIA, CallingConvention = CallingConvention.Cdecl)]
 		public extern static sk_paint_t sk_paint_new();

skia

@@ -1 +1 @@
-Subproject commit 4c78a3f640ba324ac0fc8609f3e7870dd7dae202
+Subproject commit e059dab91769c3de9e15133ec1d855a93d40c693