Properly enable base::bits::IsPowerOfTwo() only for integral types.

As explained by jdoerrie@ here:
https://crrev.com/c/2253564/4/base/pickle.cc

Change-Id: Ie36ac8f031d261819a9e9226f7226be1b6247898
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315418
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791638}

base/bits.h

@@ -25,8 +25,7 @@ namespace base {
 namespace bits {
 
 // Returns true iff |value| is a power of 2.
-template <typename T,
-          typename = typename std::enable_if<std::is_integral<T>::value>>
+template <typename T, typename = std::enable_if_t<std::is_integral<T>::value>>
 constexpr bool IsPowerOfTwo(T value) {
   // From "Hacker's Delight": Section 2.1 Manipulating Rightmost Bits.
   //