[cleanup] Mark extensions methods in subclasses with override.

Fixing clang-tidy warning.

Bug: v8:8015
Change-Id: I62ef9a644bd8ba68c44e8e224e54e8c20c3442c7
Reviewed-on: https://chromium-review.googlesource.com/1225795Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Florian Sattler <sattlerf@google.com>
Cr-Commit-Position: refs/heads/master@{#55929}

src/extensions/externalize-string-extension.cc

@@ -20,11 +20,11 @@ class SimpleStringResource : public Base {
       : data_(data),
         length_(length) {}
 
-  virtual ~SimpleStringResource() { delete[] data_; }
+  ~SimpleStringResource() override { delete[] data_; }
 
-  virtual const Char* data() const { return data_; }
+  const Char* data() const override { return data_; }
 
-  virtual size_t length() const { return length_; }
+  size_t length() const override { return length_; }
 
  private:
   Char* const data_;

src/extensions/externalize-string-extension.h

@@ -13,8 +13,8 @@ namespace internal {
 class ExternalizeStringExtension : public v8::Extension {
  public:
   ExternalizeStringExtension() : v8::Extension("v8/externalize", kSource) {}
-  virtual v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
-      v8::Isolate* isolate, v8::Local<v8::String> name);
+  v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
+      v8::Isolate* isolate, v8::Local<v8::String> name) override;
   static void Externalize(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void IsOneByte(const v8::FunctionCallbackInfo<v8::Value>& args);
 

src/extensions/free-buffer-extension.h

@@ -14,8 +14,8 @@ class FreeBufferExtension : public v8::Extension {
  public:
   FreeBufferExtension()
       : v8::Extension("v8/free-buffer", "native function freeBuffer();") {}
-  virtual v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
-      v8::Isolate* isolate, v8::Local<v8::String> name);
+  v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
+      v8::Isolate* isolate, v8::Local<v8::String> name) override;
   static void FreeBuffer(const v8::FunctionCallbackInfo<v8::Value>& args);
 };
 

src/extensions/gc-extension.h

@@ -16,8 +16,8 @@ class GCExtension : public v8::Extension {
   explicit GCExtension(const char* fun_name)
       : v8::Extension("v8/gc",
                       BuildSource(buffer_, sizeof(buffer_), fun_name)) {}
-  virtual v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
-      v8::Isolate* isolate, v8::Local<v8::String> name);
+  v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
+      v8::Isolate* isolate, v8::Local<v8::String> name) override;
   static void GC(const v8::FunctionCallbackInfo<v8::Value>& args);
 
  private:

src/extensions/statistics-extension.h

@@ -13,8 +13,8 @@ namespace internal {
 class StatisticsExtension : public v8::Extension {
  public:
   StatisticsExtension() : v8::Extension("v8/statistics", kSource) {}
-  virtual v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
-      v8::Isolate* isolate, v8::Local<v8::String> name);
+  v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
+      v8::Isolate* isolate, v8::Local<v8::String> name) override;
   static void GetCounters(const v8::FunctionCallbackInfo<v8::Value>& args);
 
  private:

src/extensions/trigger-failure-extension.h

@@ -13,8 +13,8 @@ namespace internal {
 class TriggerFailureExtension : public v8::Extension {
  public:
   TriggerFailureExtension() : v8::Extension("v8/trigger-failure", kSource) {}
-  virtual v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
-      v8::Isolate* isolate, v8::Local<v8::String> name);
+  v8::Local<v8::FunctionTemplate> GetNativeFunctionTemplate(
+      v8::Isolate* isolate, v8::Local<v8::String> name) override;
   static void TriggerCheckFalse(
       const v8::FunctionCallbackInfo<v8::Value>& args);
   static void TriggerAssertFalse(