Roll Observatory packages and add a roll script

packages/dart_style/test/regression/0000/0013.unit

+40 columns                              |
+>>> no trailing whitespace before initializer comment
+class A {
+  A()
+      // comment
+      : field = value;
+}
+<<<
+class A {
+  A()
+      // comment
+      : field = value;
+}
+>>> no trailing whitespace before initializer comment when params wrap
+class A {
+  A(some, very, long, parameter, list, that, wraps)
+      // comment
+      : field = value;
+}
+<<<
+class A {
+  A(some, very, long, parameter, list,
+      that, wraps)
+      // comment
+      : field = value;
+}