Fix Wfinal-dtor-non-final-class in plugin tests.

clang r370594 added a warning on non-final classes with final dtors.
One plugin test has code like this; just add final to these classes.

TBR=dcheng

Bug: 999869
Change-Id: I0eff3f561530b28855f21fd0c0e421613e86aa58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1778974Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692384}

tools/clang/plugins/tests/virtual_specifiers.cpp

@@ -27,7 +27,7 @@ class CorrectOverride : public Base {
   void F() OVERRIDE {}
 };
 
-class CorrectFinal : public CorrectOverride {
+class CorrectFinal FINAL : public CorrectOverride {
  public:
   ~CorrectFinal() FINAL {}
   void F() FINAL {}
@@ -47,19 +47,19 @@ class VirtualAndOverride : public Base {
   virtual void F() OVERRIDE {}
 };
 
-class VirtualAndFinal : public Base {
+class VirtualAndFinal FINAL : public Base {
  public:
   virtual ~VirtualAndFinal() FINAL {}
   virtual void F() FINAL {}
 };
 
-class VirtualAndOverrideFinal : public Base {
+class VirtualAndOverrideFinal FINAL : public Base {
  public:
   virtual ~VirtualAndOverrideFinal() OVERRIDE FINAL {}
   virtual void F() OVERRIDE FINAL {}
 };
 
-class OverrideAndFinal : public Base {
+class OverrideAndFinal FINAL : public Base {
  public:
   ~OverrideAndFinal() OVERRIDE FINAL {}
   void F() OVERRIDE FINAL {}