Remove a few friend lines referring to nonexistent classes.

I noticed these while looking at -Wmicrosoft warnings:

..\..\components/history/core/browser/history_service.h(547,16) :
   warning(clang): unqualified friend declaration referring to type outside of
                   the nearest enclosing namespace is a Microsoft extension;
                   add a nested name specifier [-Wmicrosoft]
  friend class PageUsageRequest;
               ^
               ::

If you have

  class A;
  namespace N {
  class B {
    friend class A;
  };
  }

then the "friend class A" declares a class A in namespace N and marks
it a friend of B (i.e. N::A is a friend of N::B). The first line also declares a
class A at global scope.

cl.exe (and clang-cl) don't follow the behavior that the standard asks for:
They see that there's a global class A, and interpret the line
"friend class A" to mean "global A is a friend of N::B". (The "correct"
way to write this is "friend class ::A"; A needs to be declared
at global scope for this to work.)

clang-cl can warn when it uses cl.exe's interpretation. When it warns, it
means that the friend line isn't needed (else things wouldn't compile
on non-Windows). (In some cases, the classes referred to by the
friend lines didn't even exist.)

No intended behavior change.

BUG=505296

Review URL: https://codereview.chromium.org/1217703003

Cr-Commit-Position: refs/heads/master@{#337665}

1 files changed, 0 insertions, 3 deletions

diff --git a/sync/syncable/syncable_id.h b/sync/syncable/syncable_id.h
index 3691d77b..932d2e6 100644
--- a/sync/syncable/syncable_id.h
+++ b/sync/syncable/syncable_id.h
@@ -14,8 +14,6 @@
 #include "base/memory/scoped_ptr.h"
 #include "sync/base/sync_export.h"
 
-class MockConnectionManager;
-
 namespace base {
 class StringValue;
 }
@@ -113,7 +111,6 @@ class SYNC_EXPORT Id {
                          sql::Statement* statement);
   SYNC_EXPORT_PRIVATE friend std::ostream& operator<<(std::ostream& out,
                                                       const Id& id);
-  friend class MockConnectionManager;
   friend class SyncableIdTest;
 
   std::string s_;