If Color constructor is passed a value > 0xFFFFFFFF, Sky crashes

We now ensure the color is <= 0xFFFFFFFF.

Fixes #245

R=ianh@google.com

Review URL: https://codereview.chromium.org/1179413008.

engine/src/flutter/tests/raw/color_bounds-expected.txt

@@ -0,0 +1,8 @@
+CONSOLE: unittest-suite-wait-for-done
+CONSOLE: PASS: paint set to black
+CONSOLE: PASS: color created with out of bounds value
+CONSOLE: PASS: color created with wildly out of bounds value
+CONSOLE: 
+CONSOLE: All 3 tests passed.
+CONSOLE: unittest-suite-success
+DONE

engine/src/flutter/tests/raw/color_bounds.dart

@@ -0,0 +1,35 @@
+import 'dart:sky' as sky;
+
+import '../resources/third_party/unittest/unittest.dart';
+import '../resources/unit.dart';
+
+void main() {
+  initUnit();
+
+  test("paint set to black", () {
+    sky.Color c = new sky.Color(0x00000000);
+    sky.Paint p = new sky.Paint();
+    p.color = c;
+    expect(c.toString(), equals('Color(0x00000000)'));
+  });
+
+  test("color created with out of bounds value", () {
+    try {
+      sky.Color c = new sky.Color(0x100 << 24);
+      sky.Paint p = new sky.Paint();
+      p.color = c;
+    } catch (e) {
+      expect(e != null, equals(true));
+    }
+  });
+
+  test("color created with wildly out of bounds value", () {
+    try {
+      sky.Color c = new sky.Color(1 << 1000000);
+      sky.Paint p = new sky.Paint();
+      p.color = c;
+    } catch (e) {
+      expect(e != null, equals(true));
+    }
+  });
+}