indent according to google-style-guide

https://google.github.io/styleguide/cppguide.html#Constructor_Initializer_Lists

```
// If the signature and initializer list are not all on one line,
// you must wrap before the colon and indent 4 spaces:
MyClass::MyClass(int var)
    : some_var_(var), some_other_var_(var + 1) {
  DoSomething();
}
```

and

```
// As with any other code block, the close curly can be on the same
// line as the open curly, if it fits.
MyClass::MyClass(int var)
    : some_var_(var) {}
```

upb/upb.h

@@ -127,15 +127,15 @@
   template <>                                                     \
   class Pointer<cppname> : public PointerBase<cppname, cppbase> { \
    public:                                                        \
-    explicit Pointer(cppname* ptr) :                              \
-    PointerBase<cppname, cppbase>(ptr) {}                         \
+    explicit Pointer(cppname* ptr)                                \
+        : PointerBase<cppname, cppbase>(ptr) {}                   \
   };                                                              \
   template <>                                                     \
   class Pointer<const cppname>                                    \
       : public PointerBase<const cppname, const cppbase> {        \
    public:                                                        \
-    explicit Pointer(const cppname* ptr) :                        \
-    PointerBase<const cppname, const cppbase>(ptr) {}             \
+    explicit Pointer(const cppname* ptr)                          \
+        : PointerBase<const cppname, const cppbase>(ptr) {}       \
   };                                                              \
   }
 
@@ -147,15 +147,15 @@
   template <>                                                                \
   class Pointer<cppname> : public PointerBase2<cppname, cppbase, cppbase2> { \
    public:                                                                   \
-    explicit Pointer(cppname* ptr) :                                         \
-    PointerBase2<cppname, cppbase, cppbase2>(ptr) {}                         \
+    explicit Pointer(cppname* ptr)                                           \
+        : PointerBase2<cppname, cppbase, cppbase2>(ptr) {}                   \
   };                                                                         \
   template <>                                                                \
   class Pointer<const cppname>                                               \
       : public PointerBase2<const cppname, const cppbase, const cppbase2> {  \
    public:                                                                   \
-    explicit Pointer(const cppname* ptr) :                                   \
-    PointerBase2<const cppname, const cppbase, const cppbase2>(ptr) {}       \
+    explicit Pointer(const cppname* ptr)                                     \
+        : PointerBase2<const cppname, const cppbase, const cppbase2>(ptr) {} \
   };                                                                         \
   }