Fix default constructor in the default implementation of QuicheMemSlice.

Fixes the standalone QUICHE build.

PiperOrigin-RevId: 698793891

quiche/common/platform/api/quiche_mem_slice_test.cc

diff --git a/quiche/common/platform/api/quiche_mem_slice_test.cc b/quiche/common/platform/api/quiche_mem_slice_test.cc
index 3d08d1e..f7e9736 100644
--- a/quiche/common/platform/api/quiche_mem_slice_test.cc
+++ b/quiche/common/platform/api/quiche_mem_slice_test.cc
@@ -33,6 +33,13 @@
   size_t orig_length_;
 };
 
+TEST_F(QuicheMemSliceTest, Empty) {
+  QuicheMemSlice empty;
+  EXPECT_EQ(empty.data(), nullptr);
+  EXPECT_EQ(empty.length(), 0);
+  EXPECT_TRUE(empty.empty());
+}
+
 TEST_F(QuicheMemSliceTest, MoveConstruct) {
   QuicheMemSlice moved(std::move(slice_));
   EXPECT_EQ(moved.data(), orig_data_);

quiche/common/platform/default/quiche_platform_impl/quiche_mem_slice_impl.h

diff --git a/quiche/common/platform/default/quiche_platform_impl/quiche_mem_slice_impl.h b/quiche/common/platform/default/quiche_platform_impl/quiche_mem_slice_impl.h
index d20ebbe..bf78b29 100644
--- a/quiche/common/platform/default/quiche_platform_impl/quiche_mem_slice_impl.h
+++ b/quiche/common/platform/default/quiche_platform_impl/quiche_mem_slice_impl.h
@@ -77,9 +77,9 @@
   bool empty() const { return size_ == 0; }
 
  private:
-  const char* data_;
-  size_t size_;
-  SingleUseCallback<void(const char*)> done_callback_;
+  const char* data_ = nullptr;
+  size_t size_ = 0;
+  SingleUseCallback<void(const char*)> done_callback_ = nullptr;
 };
 
 }  // namespace quiche