Make :rtc_base_approved a public dep of :rtc_base.

It looks to me like targets :rtc_base_approved is logically a subset of
:rtc_base, and so any targets depending on :rtc_base expect to also get
access to the headers in :rtc_base_approved.

Thus I think it's appropriate for :rtc_base to have :rtc_base_approved in
public_deps, so that `gn check` will permit this without clients having to
explicitly depend on both.

NOTRY=True

Review URL: https://codereview.webrtc.org/1578833002

Cr-Commit-Position: refs/heads/master@{#11227}

webrtc/base/BUILD.gn

@@ -177,7 +177,8 @@ static_library("rtc_base") {
   cflags = []
   cflags_cc = []
   libs = []
-  deps = [
+  deps = []
+  public_deps = [
     ":rtc_base_approved",
   ]
 

webrtc/base/base.gyp

@@ -152,6 +152,9 @@
         '<(webrtc_root)/common.gyp:webrtc_common',
         'rtc_base_approved',
       ],
+      'export_dependent_settings': [
+        'rtc_base_approved',
+      ],
       'defines': [
         'FEATURE_ENABLE_SSL',
         'SSL_USE_OPENSSL',