cppgc: Reduce the age table back to 1MB

The increase caused a significant PMF regression on Windows. Apparently,
leaving the table in reserved state didn't eliminate the regression. The
CL returns the age size back to 1MB. The followup is to investiage and
fix the regression.

Bug: chromium:1336420
Change-Id: I56542ba4efe0fc8d08d8c5febf758384559a8860
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3758146Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81705}

include/cppgc/internal/caged-heap-local-data.h

@@ -33,7 +33,7 @@ class HeapBase;
 // regions (cards). Each entry in the table represents generation of the objects
 // that reside on the corresponding card (young, old or mixed).
 class V8_EXPORT AgeTable final {
-  static constexpr size_t kRequiredSize = 8 * api_constants::kMB;
+  static constexpr size_t kRequiredSize = 1 * api_constants::kMB;
   static constexpr size_t kAllocationGranularity =
       api_constants::kAllocationGranularity;
 
@@ -72,7 +72,7 @@ class V8_EXPORT AgeTable final {
         __builtin_ctz(static_cast<uint32_t>(kCardSizeInBytes));
 #else   //! V8_HAS_BUILTIN_CTZ
         // Hardcode and check with assert.
-        9;
+        12;
 #endif  // !V8_HAS_BUILTIN_CTZ
     static_assert((1 << kGranularityBits) == kCardSizeInBytes);
     const size_t entry = offset >> kGranularityBits;
@@ -83,8 +83,8 @@ class V8_EXPORT AgeTable final {
   std::array<Age, kRequiredSize> table_;
 };
 
-static_assert(sizeof(AgeTable) == 8 * api_constants::kMB,
-              "Size of AgeTable is 8MB");
+static_assert(sizeof(AgeTable) == 1 * api_constants::kMB,
+              "Size of AgeTable is 1MB");
 
 #endif  // CPPGC_YOUNG_GENERATION