[dawn] Try to fix raw_ptr usage in DynamicLib

Bug: 486928687, 485825675
Change-Id: I29776ff5380ecd5849c592cb9872fa0c280c0da1
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/293095
Reviewed-by: Peter McNeeley <petermcneeley@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Peter McNeeley <petermcneeley@google.com>

src/dawn/common/DynamicLib.h

diff --git a/src/dawn/common/DynamicLib.h b/src/dawn/common/DynamicLib.h
index 4b8fdfd..98ba1aa 100644
--- a/src/dawn/common/DynamicLib.h
+++ b/src/dawn/common/DynamicLib.h
@@ -34,7 +34,14 @@
 
 #include "dawn/common/Assert.h"
 #include "dawn/common/Platform.h"
+
+#if DAWN_PLATFORM_IS(WINDOWS)
 #include "partition_alloc/pointers/raw_ptr.h"
+#elif DAWN_PLATFORM_IS(POSIX)
+#include "partition_alloc/pointers/raw_ptr_exclusion.h"
+#else
+#error "Unsupported platform for DynamicLib"
+#endif
 
 namespace dawn {
 
@@ -73,8 +80,18 @@
     }
 
   private:
-    // TODO(crbug.com/485825675): Investigate why this pointer is dangling.
-    raw_ptr<void, DanglingUntriaged> mHandle = nullptr;
+#if DAWN_PLATFORM_IS(WINDOWS)
+    // This is an HMODULE (aka void*). It should point to real memory, so we can use raw_ptr:
+    // > A handle to a module. This is the base address of the module in memory.
+    raw_ptr<void> mHandle = nullptr;
+#elif DAWN_PLATFORM_IS(POSIX)
+    // On POSIX we use `dlopen`, which returns a "handle" which may not be a real pointer:
+    // > The value of this symbol table handle should not be interpreted in any way by the caller.
+    RAW_PTR_EXCLUSION void* mHandle = nullptr;
+#else
+#error "Unsupported platform for DynamicLib"
+#endif
+
     bool mNeedsClose = false;
 };