Convert the no-inline-virtuals rule into a constructors rule.

tools/clang/plugins/tests/virtual_bodies.txt

 In file included from virtual_bodies.cpp:5:
-./virtual_bodies.h:23:36: warning: [chromium-style] virtual methods with non-empty bodies shouldn't be declared inline.
-  virtual bool ComplainAboutThis() { return true; }
-                                   ^
-1 warning generated.
+./virtual_bodies.h:17:1: warning: [chromium-style] Complex class/struct needs an explicit out-of-line constructor.
+class InlineVirtualMethodsInHeaders {
+^
+./virtual_bodies.h:28:1: warning: [chromium-style] Complex class/struct needs an explicit out-of-line constructor.
+class LongInlineVirtualMethods {
+^
+./virtual_bodies.h:83:1: warning: [chromium-style] Complex class/struct needs an explicit out-of-line constructor.
+class InlineVirtualMethodsInLeafClass
+^
+./virtual_bodies.h:93:3: warning: [chromium-style] Complex destructor has an inline body.
+  ~DtorInlineVirtualMethodsInHeaders() {}
+  ^
+4 warnings generated.