Summary:
Add decent blank lines between declarations:
* Add extra blank line after #define or #includes.
* Add extra blank line between declarations.
* Add extra blank line in front of #endif.

Previously, the new generated code is quite tight:

```
#ifndef FOO_H
#define FOO_H
namespace a {
class A { public: int f(); };
int A::f() { return 0; }
} // namespace a
#endif // FOO_H
```

After this patch, the code looks like:

```
#ifndef FOO_H
#define FOO_H

namespace a {
class A { public: int f(); };

int A::f() { return 0; }
} // namespace a

#endif // FOO_H
```

Reviewers: ioeric

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D26493

llvm-svn: 286943