Enable ClangTidy flag modernize-use-override.

https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-override.html

Adds override (introduced in C++11) to overridden virtual functions and
removes virtual from those functions as it is not required.

virtual on non base class implementations was used to help indicate to
the user that a function was virtual. C++ compilers did not use the
presence of this to signify an overridden function.

Change-Id: If66d8919358f72a4035190caf8d7569268037a9a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/310160
Commit-Queue: Mike Klein <mtklein@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/.clang-tidy b/.clang-tidy
index 5160dd6..7c4b363 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -1,4 +1,20 @@
-Checks: '-*,bugprone-use-after-move,bugprone-unused-raii,bugprone-undelegated-constructor,bugprone-argument-comment,bugprone-bool-pointer-implicit-conversion,performance-unnecessary-copy-initialization,performance-for-range-copy,readability-redundant-preprocessor,misc-definitions-in-headers,modernize-make-unique,llvm-namespace-comment,readability-static-accessed-through-instance,readability-const-return-type,google-build-namespaces'
+Checks: >
+    -*,
+    bugprone-argument-comment,
+    bugprone-bool-pointer-implicit-conversion,
+    bugprone-undelegated-constructor,
+    bugprone-unused-raii,
+    bugprone-use-after-move,
+    google-build-namespaces,
+    llvm-namespace-comment,
+    misc-definitions-in-headers,
+    modernize-make-unique,
+    modernize-use-override,
+    performance-for-range-copy,
+    performance-unnecessary-copy-initialization,
+    readability-const-return-type,
+    readability-redundant-preprocessor,
+    readability-static-accessed-through-instance
 CheckOptions:
   - key:             llvm-namespace-comment.SpacesBeforeComments
     value:           2