Adds fbounds annotations for VP8LColorCache.

Reasoning:

Analysis of `VP8LColorCacheInit`
(src/utils/color_cache_utils.c:29) revealed that `colors` is allocated
using `WebPSafeCalloc` with a size of `1 << hash_bits`. Therefore,
`colors` was annotated with `WEBP_COUNTED_BY_OR_NULL(1u << hash_bits)`.
To support this, `WebPSafeCalloc` (src/utils/utils.h:59,
src/utils/utils.c:214) was annotated to return
`WEBP_SIZED_BY_OR_NULL(nmemb * size)`. Since `WebPSafeCalloc` returns a
local pointer that defaults to unsafe when bounds safety is suppressed,
`WEBP_UNSAFE_FORGE_BIDI_INDEXABLE` was used on the return value
(src/utils/utils.c:222). Similarly, `VP8LColorCacheInit` required
`WEBP_UNSAFE_FORGE_BIDI_INDEXABLE` when assigning the allocated pointer
to the struct field (src/utils/color_cache_utils.c:47). Finally,
`VP8LColorCacheInit` and `VP8LColorCacheClear` were modified to perform
side-by-side assignments to `colors` and `hash_bits` as required by the
`WEBP_COUNTED_BY_OR_NULL` annotation, using self-assignment for
`hash_bits` when necessary to maintain functional equivalence with the
original code.

Bug: 432511821
Change-Id: I63cb46909d883a2e8932043ac3117b05b37e8d40

src/utils/color_cache_utils.c

@@ -28,13 +28,19 @@ WEBP_ASSUME_UNSAFE_INDEXABLE_ABI
 
 int VP8LColorCacheInit(VP8LColorCache* const color_cache, int hash_bits) {
   const int hash_size = 1 << hash_bits;
+  uint32_t* colors = (uint32_t*)WebPSafeCalloc((uint64_t)hash_size,
+                                               sizeof(*color_cache->colors));
   assert(color_cache != NULL);
   assert(hash_bits > 0);
-  color_cache->colors = (uint32_t*)WebPSafeCalloc((uint64_t)hash_size,
-                                                  sizeof(*color_cache->colors));
-  if (color_cache->colors == NULL) return 0;
+  if (colors == NULL) {
+    color_cache->colors = NULL;
+    WEBP_SELF_ASSIGN(color_cache->hash_bits);
+    return 0;
+  }
   color_cache->hash_shift = 32 - hash_bits;
   color_cache->hash_bits = hash_bits;
+  color_cache->colors = WEBP_UNSAFE_FORGE_BIDI_INDEXABLE(
+      uint32_t*, colors, (size_t)hash_size * sizeof(*color_cache->colors));
   return 1;
 }
 
@@ -42,6 +48,7 @@ void VP8LColorCacheClear(VP8LColorCache* const color_cache) {
   if (color_cache != NULL) {
     WebPSafeFree(color_cache->colors);
     color_cache->colors = NULL;
+    WEBP_SELF_ASSIGN(color_cache->hash_bits);
   }
 }
 

src/utils/color_cache_utils.h

@@ -30,8 +30,8 @@ extern "C" {
 
 // Main color cache struct.
 typedef struct {
-  uint32_t* colors;  // color entries
-  int hash_shift;    // Hash shift: 32 - 'hash_bits'.
+  uint32_t* WEBP_COUNTED_BY_OR_NULL(1u << hash_bits) colors;  // color entries
+  int hash_shift;  // Hash shift: 32 - 'hash_bits'.
   int hash_bits;
 } VP8LColorCache;
 

src/utils/utils.c

@@ -211,14 +211,15 @@ void* WebPSafeMalloc(uint64_t nmemb, size_t size) {
   return ptr;
 }
 
-void* WebPSafeCalloc(uint64_t nmemb, size_t size) {
+void* WEBP_SIZED_BY_OR_NULL(nmemb* size)
+    WebPSafeCalloc(uint64_t nmemb, size_t size) {
   void* ptr;
   Increment(&num_calloc_calls);
   if (!CheckSizeArgumentsOverflow(nmemb, size)) return NULL;
   assert(nmemb * size > 0);
   ptr = calloc((size_t)nmemb, size);
   AddMem(ptr, (size_t)(nmemb * size));
-  return ptr;
+  return WEBP_UNSAFE_FORGE_BIDI_INDEXABLE(void*, ptr, (size_t)(nmemb * size));
 }
 
 void WebPSafeFree(void* const ptr) {

src/utils/utils.h

@@ -56,7 +56,8 @@ static WEBP_INLINE int CheckSizeOverflow(uint64_t size) {
 WEBP_EXTERN void* WebPSafeMalloc(uint64_t nmemb, size_t size);
 // Note that WebPSafeCalloc() expects the second argument type to be 'size_t'
 // in order to favor the "calloc(num_foo, sizeof(foo))" pattern.
-WEBP_EXTERN void* WebPSafeCalloc(uint64_t nmemb, size_t size);
+WEBP_EXTERN void* WEBP_SIZED_BY_OR_NULL(nmemb* size)
+    WebPSafeCalloc(uint64_t nmemb, size_t size);
 
 // Companion deallocation function to the above allocations.
 WEBP_EXTERN void WebPSafeFree(void* const ptr);