Add extra checks to avoid integer overflow.

BUG=425980
TEST=no crash with ASAN

Review URL: https://codereview.chromium.org/659743004

Cr-Commit-Position: refs/heads/master@{#301249}
static uint32 Read24(const uint8* p) {
  return p[0] << 16 | p[1] << 8 | p[2];
}

static uint32 Read24(const uint8* p) {
  return p[0] << 16 | p[1] << 8 | p[2];
}
