Build SharedExclusiveLock in Chromium.

Partially un-breaks the Chromium FYI build.

TBR=jbauch@webrtc.org, tommi@webrtc.org
BUG=

Review URL: https://codereview.webrtc.org/1739713002 .

Cr-Original-Commit-Position: refs/heads/master@{#11765}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a5d8e4eef58574ddb4c4c818de71491a52887f45
diff --git a/base/base.gyp b/base/base.gyp
index cb1eac4..18e4adf 100644
--- a/base/base.gyp
+++ b/base/base.gyp
@@ -499,8 +499,6 @@
             'safe_conversions_impl.h',
             'scopedptrcollection.h',
             'sec_buffer.h',
-            'sharedexclusivelock.cc',
-            'sharedexclusivelock.h',
             'sslconfig.h',
             'sslroots.h',
             'testbase64.h',