Implement addPath() method for Path object

LayoutTests/fast/canvas/script-tests/canvas-path-addpath.js

+description("Test addPath() method.");
+var ctx = document.createElement('canvas').getContext('2d');
+
+debug("Test addPath() with transform as identity matrix.")
+ctx.beginPath();
+var p1 = new Path();
+p1.rect(0,0,100,100);
+var p2 = new Path();
+p2.rect(0,100,100,100);
+var m = ctx.currentTransform;
+p1.addPath(p2, m);
+ctx.fillStyle = 'yellow';
+ctx.currentPath = p1;
+ctx.fill();
+var imageData = ctx.getImageData(0, 100, 100, 100);
+var imgdata = imageData.data;
+shouldBe("imgdata[4]", "255");
+shouldBe("imgdata[5]", "255");
+shouldBe("imgdata[6]", "0");
+shouldBe("imgdata[7]", "255");
+debug("");
+
+debug("Test addPath() with transform as translate(100, -100).")
+ctx.beginPath();
+var p3 = new Path();
+p3.rect(0,0,100,100);
+var p4 = new Path();
+p4.rect(0,100,100,100);
+m.a = 1; m.b = 0;
+m.c = 0; m.d = 1;
+m.e = 100; m.f = -100;
+p3.addPath(p4, m);
+ctx.fillStyle = 'yellow';
+ctx.currentPath = p3;
+ctx.fill();
+var imageData = ctx.getImageData(100, 0, 100, 100);

[Justin Novosad, 2014/02/19 16:38:28]

no need for 'var' here. Same thing for following line.

[pals, 2014/03/03 06:27:39]

Done.

+var imgdata = imageData.data;
+shouldBe("imgdata[4]", "255");
+shouldBe("imgdata[5]", "255");
+shouldBe("imgdata[6]", "0");
+shouldBe("imgdata[7]", "255");
+debug("");
+
+debug("Test addPath() with non-invertible transform.")
+ctx.beginPath();
+var p5 = new Path();
+p5.rect(0,0,100,100);
+var p6 = new Path();
+p6.rect(100,100,100,100);
+m.a = 0; m.b = 0;
+m.c = 0; m.d = 0;
+m.e = 0; m.f = 0;
+p5.addPath(p6, m);
+ctx.fillStyle = 'yellow';
+ctx.currentPath = p5;
+ctx.fill();
+var imageData = ctx.getImageData(100, 100, 100, 100);

[Justin Novosad, 2014/02/19 16:38:28]

Same here.

[pals, 2014/03/03 06:27:39]

Done.

+var imgdata = imageData.data;
+shouldNotBe("imgdata[4]", "255");
+shouldNotBe("imgdata[5]", "255");
+shouldBe("imgdata[6]", "0");
+shouldNotBe("imgdata[7]", "255");
+debug("");
+
+debug("Test addPath() with transform as null.")
+var p7 = new Path();
+p7.rect(0,0,100,100);
+var p8 = new Path();
+shouldThrow("p7.addPath(p8, null)");
+debug("");