GWP-ASan: Delete unnecessary function

The custom version of bits::CountTrailingZeroBits64 is deprecated by
upstream support from https://crrev.com/c/1321253

Change-Id: Id091afc2c5bd2d8ba8969ec12248b4c89d4d9ee1
Reviewed-on: https://chromium-review.googlesource.com/c/1355248
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612502}

components/gwp_asan/client/guarded_page_allocator.cc

@@ -136,7 +136,7 @@ size_t GuardedPageAllocator::ReserveSlot() {
   uint64_t rot = base::RandGenerator(AllocatorState::kGpaMaxPages);
   BitMap rotated_bitmap = (free_pages_ << rot) |
                           (free_pages_ >> (AllocatorState::kGpaMaxPages - rot));
-  int rotated_selection = CountTrailingZeroBits64(rotated_bitmap);
+  int rotated_selection = base::bits::CountTrailingZeroBits(rotated_bitmap);
   size_t selection = (rotated_selection - rot + AllocatorState::kGpaMaxPages) %
                      AllocatorState::kGpaMaxPages;
   DCHECK_LT(selection, AllocatorState::kGpaMaxPages);

components/gwp_asan/client/guarded_page_allocator.h

@@ -18,11 +18,6 @@
 namespace gwp_asan {
 namespace internal {
 
-// Method to count trailing zero bits in a uint64_t (identical to
-// base::bits::CountTrailingZeroBits64 except that it also works on 32-bit
-// platforms.)
-unsigned CountTrailingZeroBits64(uint64_t x);
-
 // This class encompasses the allocation and deallocation logic on top of the
 // AllocatorState. Its members are not inspected or used by the crash handler.
 class GWP_ASAN_EXPORT GuardedPageAllocator {

components/gwp_asan/client/guarded_page_allocator_win.cc

@@ -6,30 +6,12 @@
 
 #include "components/gwp_asan/client/guarded_page_allocator.h"
 
-#include "base/bits.h"
 #include "base/logging.h"
 #include "build/build_config.h"
 
 namespace gwp_asan {
 namespace internal {
 
-unsigned CountTrailingZeroBits64(uint64_t x) {
-#if defined(ARCH_CPU_64_BITS)
-  return base::bits::CountTrailingZeroBits(x);
-#else
-  // Windows 32-bit builds do not support CountTrailingZeroBits on a uint64_t.
-  // TODO(vtsyrklevich): Fix this in base::bits instead.
-  uint32_t right = static_cast<uint32_t>(x);
-  unsigned right_trailing = base::bits::CountTrailingZeroBits(right);
-  if (right_trailing < 32)
-    return right_trailing;
-
-  uint32_t left = static_cast<uint32_t>(x >> 32);
-  unsigned left_trailing = base::bits::CountTrailingZeroBits(left);
-  return left_trailing + right_trailing;
-#endif
-}
-
 // TODO(vtsyrklevich): See if the platform-specific memory allocation and
 // protection routines can be broken out in base/ and merged with those used for
 // PartionAlloc/ProtectedMemory.