Revert of Allow std::unordered_*. (patchset #15 id:280001 of https://codereview.chromium.org/1502373009/ )

Reason for revert:
MSan build failure.

https://build.chromium.org/p/chromium.memory.fyi/builders/Chromium%20Linux%20ChromeOS%20MSan%20Builder/builds/12498

Original issue's description:
> Allow std::unordered_*.
>
> base::hash_* is, as a transition step, implemented in terms of
> std::unordered_*. Later commits will convert existing uses.
>
> Also fix a host of IWYU problems that arose from this CL.
>
> (NOPRESUBMIT because the wstring presubmit check is overzealous
> and complains about the reference to wstring in the comment.)
>
> NOPRESUBMIT=true
> BUG=576864
> TBR=derat@chromium.org,blundell@chromium.org,jbauman@chromium.org,dalecurtis@chromium.org
> CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
>
> Committed: https://crrev.com/3f37f7f1459e7b5a452c0e433493e0a6e9649ca7
> Cr-Commit-Position: refs/heads/master@{#370553}

TBR=danakj@chromium.org,thakis@chromium.org,derat@chromium.org,blundell@chromium.org,dalecurtis@chromium.org,jbauman@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=576864

Review URL: https://codereview.chromium.org/1610023003

Cr-Commit-Position: refs/heads/master@{#370559}

1 files changed, 3 insertions, 11 deletions

diff --git a/base/strings/string16_unittest.cc b/base/strings/string16_unittest.cc
index 0d2ca80..4e58218 100644
--- a/base/strings/string16_unittest.cc
+++ b/base/strings/string16_unittest.cc
@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 #include <sstream>
-#include <unordered_set>
 
 #include "base/strings/string16.h"
 
@@ -12,6 +11,8 @@
 
 namespace base {
 
+#if defined(WCHAR_T_IS_UTF32)
+
 // We define a custom operator<< for string16 so we can use it with logging.
 // This tests that conversion.
 TEST(String16Test, OutputStream) {
@@ -52,15 +53,6 @@ TEST(String16Test, OutputStream) {
   }
 }
 
-TEST(String16Test, Hash) {
-  string16 str1 = ASCIIToUTF16("hello");
-  string16 str2 = ASCIIToUTF16("world");
-
-  std::unordered_set<string16> set;
-
-  set.insert(str1);
-  EXPECT_EQ(1u, set.count(str1));
-  EXPECT_EQ(0u, set.count(str2));
-}
+#endif
 
 }  // namespace base