[Code Health] Remove a use of base::SupportsWeakPtr. (storage)

This CL replaces the base class with a base::WeakPtrFactory data
member and an accessor member function.

Bug: 40485134
Change-Id: I4a6f88fe209938019eba454f06c6aee2b8faaf57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5578738
Commit-Queue: Ayu Ishii <ayui@chromium.org>
Reviewed-by: Ayu Ishii <ayui@chromium.org>
Auto-Submit: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1307507}

storage/browser/test/mock_blob_registry_delegate.cc

@@ -7,6 +7,9 @@
 
 namespace storage {
 
+MockBlobRegistryDelegate::MockBlobRegistryDelegate() = default;
+MockBlobRegistryDelegate::~MockBlobRegistryDelegate() = default;
+
 bool MockBlobRegistryDelegate::CanReadFile(const base::FilePath& file) {
   return can_read_file_result;
 }

storage/browser/test/mock_blob_registry_delegate.h

@@ -10,18 +10,23 @@
 
 namespace storage {
 
-class MockBlobRegistryDelegate
-    : public BlobRegistryImpl::Delegate,
-      public base::SupportsWeakPtr<MockBlobRegistryDelegate> {
+class MockBlobRegistryDelegate final : public BlobRegistryImpl::Delegate {
  public:
-  MockBlobRegistryDelegate() = default;
-  ~MockBlobRegistryDelegate() override = default;
+  MockBlobRegistryDelegate();
+  ~MockBlobRegistryDelegate() override;
 
   bool CanReadFile(const base::FilePath& file) override;
   bool CanAccessDataForOrigin(const url::Origin& origin) override;
 
   bool can_read_file_result = true;
   bool can_access_data_for_origin = true;
+
+  base::WeakPtr<MockBlobRegistryDelegate> AsWeakPtr() {
+    return weak_ptr_factory_.GetWeakPtr();
+  }
+
+ private:
+  base::WeakPtrFactory<MockBlobRegistryDelegate> weak_ptr_factory_{this};
 };
 
 }  // namespace storage