Extract rtc_base/base64.h and rtc_base/base64.cc into separate target.

Extract rtc_base/base64.h and rtc_base/base64.cc into separate target
to prepare to move them into third_party

Bug: webrtc:8366
Change-Id: I477e6da2b9d09307439b3272261f31042f479d74
Reviewed-on: https://webrtc-review.googlesource.com/83980
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23645}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 79db4f4..bcca552 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -368,6 +368,7 @@
   data_deps = []
   deps = [
     ":atomicops",
+    ":base64",
     ":checks",
     ":criticalsection",
     ":logging",
@@ -389,8 +390,6 @@
   ]
 
   sources = [
-    "base64.cc",
-    "base64.h",
     "bind.h",
     "bitbuffer.cc",
     "bitbuffer.h",
@@ -490,6 +489,18 @@
   }
 }
 
+rtc_source_set("base64") {
+  visibility = [ "*" ]
+  sources = [
+    "base64.cc",
+    "base64.h",
+  ]
+
+  deps = [
+    ":checks",
+  ]
+}
+
 rtc_source_set("rtc_task_queue") {
   visibility = [ "*" ]
   deps = []
@@ -712,6 +723,7 @@
   libs = []
   defines = []
   deps = [
+    ":base64",
     ":checks",
     ":stringutils",
     "..:webrtc_common",
@@ -1152,6 +1164,7 @@
       sources += [ "win/windows_version_unittest.cc" ]
     }
     deps = [
+      ":base64",
       ":checks",
       ":rate_limiter",
       ":rtc_base",