add support for custom Java Drawables

This is made possible, by adding a second Canvas implementation which
can be used to render directly to GdkSnapshot objects

For now the only implemented method is drawBitmap(), this is already
enough to make VectorDrawableCompat functional

src/api-impl/android/graphics/GskCanvas.java

@@ -0,0 +1,74 @@
+package android.graphics;
+
+/**
+ * GskCanvas:
+ *   - implements Canvas for onscreen rendering inside GTKs snapshot function
+ */
+public class GskCanvas extends Canvas {
+	private long snapshot;
+
+	public GskCanvas(long snapshot) {
+		System.out.println("GskCanvas(" + snapshot + ")");
+		this.snapshot = snapshot;
+	}
+
+	@Override
+	public int save() {
+		System.out.println("GskCanvas.save()");
+		return -1;
+	}
+
+	@Override
+	public void restore() {
+		System.out.println("GskCanvas.restore()");
+	}
+
+	@Override
+	public void translate(float dx, float dy) {
+		System.out.println("GskCanvas.translate(" + dx + ", " + dy + ")");
+	}
+
+	@Override
+	public void rotate(float degrees) {
+		System.out.println("GskCanvas.rotate(" + degrees + ")");
+	}
+
+	@Override
+	public void drawBitmap(Bitmap bitmap, Rect src, Rect dst, Paint paint) {
+		native_drawBitmap(snapshot, bitmap.pixbuf, dst.left, dst.top, dst.width(), dst.height());
+	}
+
+	@Override
+	public void drawPath(Path path, Paint paint) {
+		System.out.println("GskCanvas.drawPath(" + path + ", " + paint + ")");
+	}
+
+	@Override
+	public void drawRect(float left, float top, float right, float bottom, Paint paint) {
+		System.out.println("GskCanvas.drawRect(" + left + ", " + top + ", " + right + ", " + bottom + ", " + paint + ")");
+	}
+
+	@Override
+	public void rotate(float degrees, float px, float py) {
+		System.out.println("GskCanvas.rotate(" + degrees + ", " + px + ", " + py + ")");
+	}
+
+	@Override
+	public void drawText(String text, float x, float y, Paint paint) {
+		System.out.println("GskCanvas.drawText(" + text + ", " + x + ", " + y + ", " + paint + ")");
+	}
+
+	@Override
+	public void drawLine(float startX, float startY, float stopX, float stopY, Paint paint) {
+		System.out.println("GskCanvas.drawLine(" + startX + ", " + startY + ", " + stopX + ", " + stopY + ", " + paint + ")");
+	}
+
+	@Override
+	public void drawBitmap(Bitmap bitmap, float left, float top, Paint paint) {
+		Rect src = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
+		Rect dst = new Rect((int)left, (int)top, (int)left + bitmap.getWidth(), (int)top + bitmap.getHeight());
+		drawBitmap(bitmap, src, dst, paint);
+	}
+
+	protected native void native_drawBitmap(long snapshot, long pixbuf, int x, int y, int width, int height);
+}