[platform] Add spanified API for Dawn's CachingInterface.

- Note we added default implementations for both the new and old
  APIs for now until downstream users are updated and we can remove
  the old ones.

Bug: 503801946
Change-Id: I55ba9ea12b1e7ba3d71f1411ea91c76965181b58
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/304738
Auto-Submit: Loko Kung <lokokung@google.com>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>

include/dawn/platform/DawnPlatform.h

diff --git a/include/dawn/platform/DawnPlatform.h b/include/dawn/platform/DawnPlatform.h
index 27067b6..e4f720f 100644
--- a/include/dawn/platform/DawnPlatform.h
+++ b/include/dawn/platform/DawnPlatform.h
@@ -33,6 +33,8 @@
 #include <cstddef>
 #include <cstdint>
 #include <memory>
+#include <span>
+#include <string_view>
 
 #include "dawn/platform/dawn_platform_export.h"
 
@@ -50,19 +52,23 @@
     CachingInterface();
     virtual ~CachingInterface();
 
-    // LoadData has two modes. The first mode is used to get a value which
-    // corresponds to the |key|. The |valueOut| is a caller provided buffer
-    // allocated to the size |valueSize| which is loaded with data of the
-    // size returned. The second mode is used to query for the existence of
-    // the |key| where |valueOut| is nullptr and |valueSize| must be 0.
-    // The return size is non-zero if the |key| exists.
-    virtual size_t LoadData(const void* key, size_t keySize, void* valueOut, size_t valueSize) = 0;
+    // Returns zero if there does not exist a cached entry for |key|, otherwise returns a non-zero
+    // size indicating the size of cached data
+    virtual size_t FindKey(std::string_view key) { return 0; }
 
-    // StoreData puts a |value| in the cache which corresponds to the |key|.
-    virtual void StoreData(const void* key,
-                           size_t keySize,
-                           const void* value,
-                           size_t valueSize) = 0;
+    // Returns zero if unable to load cached entry for |key| into |dest|, otherwise returns number
+    // of bytes written to |dest|.
+    virtual size_t LoadData(std::string_view key, std::span<uint8_t> dest) { return 0; }
+
+    // Stores the data in |src| at the entry specified by |key|.
+    virtual void StoreData(std::string_view key, std::span<const uint8_t> src) {}
+
+    // TODO(503801946): Remove these outdated default implementations and make the newer API above
+    // fully virtual once users are updated.
+    virtual size_t LoadData(const void* key, size_t keySize, void* valueOut, size_t valueSize) {
+        return 0;
+    }
+    virtual void StoreData(const void* key, size_t keySize, const void* value, size_t valueSize) {}
 
   private:
     CachingInterface(const CachingInterface&) = delete;