Revert of Remove remains of webrtc/base (patchset #7 id:120001 of https://codereview.webrtc.org/2973183002/ )

Reason for revert:
Breaks lots of downstream projects.

Original issue's description:
> Remove remains of webrtc/base
>
> All downstream code have been updated to the new location.
>
> In PRESUBMIT.py:
> * Remove webrtc/rtc_base from CPP_BLACKLIST
> * Add webrtc/rtc_base to LEGACY_API_DIRS
>
> Fix some duplicated paths in
> webrtc/modules/audio_processing/test/conversational_speech/BUILD.gn
>
> BUG=webrtc:7634
> TBR=kwiberg@webrtc.org
>
> Review-Url: https://codereview.webrtc.org/2973183002
> Cr-Commit-Position: refs/heads/master@{#18948}
> Committed:
https://chromium.googlesource.com/external/webrtc/+/9483b49bafc681a8360dff7217e7651a74dea71d

TBR=kwiberg@webrtc.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:7634

Review-Url: https://codereview.webrtc.org/2976633002
Cr-Original-Commit-Position: refs/heads/master@{#18949}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 370dd479730b4918b8b81842c4c36d25d0633b50
diff --git a/examples/BUILD.gn b/examples/BUILD.gn
index 55b72dd..85813fa 100644
--- a/examples/BUILD.gn
+++ b/examples/BUILD.gn
@@ -422,7 +422,7 @@
           "objc/AppRTCMobile/tests/ARDSettingsModel_xctest.mm",
         ]
         deps = [
-          "//webrtc/rtc_base:rtc_base",
+          "//webrtc/base:rtc_base",
         ]
         public_deps = [
           ":AppRTCMobile_ios_frameworks",
@@ -524,12 +524,12 @@
       "//third_party/libyuv",
       "//webrtc/api:libjingle_peerconnection_test_api",
       "//webrtc/api:video_frame_api",
+      "//webrtc/base:rtc_base",
+      "//webrtc/base:rtc_base_approved",
+      "//webrtc/base:rtc_json",
       "//webrtc/media:rtc_media",
       "//webrtc/modules/video_capture:video_capture_module",
       "//webrtc/pc:libjingle_peerconnection",
-      "//webrtc/rtc_base:rtc_base",
-      "//webrtc/rtc_base:rtc_base_approved",
-      "//webrtc/rtc_base:rtc_json",
       "//webrtc/system_wrappers:field_trial_default",
       "//webrtc/system_wrappers:metrics_default",
     ]
@@ -548,7 +548,7 @@
     ]
     deps = [
       "//webrtc:webrtc_common",
-      "//webrtc/rtc_base:rtc_base_approved",
+      "//webrtc/base:rtc_base_approved",
       "//webrtc/rtc_tools:command_line_parser",
     ]
     if (!build_with_chromium && is_clang) {
@@ -562,10 +562,10 @@
       "relayserver/relayserver_main.cc",
     ]
     deps = [
-      "../rtc_base:rtc_base",
+      "../base:rtc_base",
+      "//webrtc/base:rtc_base_approved",
       "//webrtc/p2p:rtc_p2p",
       "//webrtc/pc:rtc_pc",
-      "//webrtc/rtc_base:rtc_base_approved",
       "//webrtc/system_wrappers:field_trial_default",
       "//webrtc/system_wrappers:metrics_default",
     ]
@@ -580,10 +580,10 @@
       "turnserver/turnserver_main.cc",
     ]
     deps = [
-      "../rtc_base:rtc_base",
+      "../base:rtc_base",
+      "//webrtc/base:rtc_base_approved",
       "//webrtc/p2p:rtc_p2p",
       "//webrtc/pc:rtc_pc",
-      "//webrtc/rtc_base:rtc_base_approved",
       "//webrtc/system_wrappers:field_trial_default",
       "//webrtc/system_wrappers:metrics_default",
     ]
@@ -598,10 +598,10 @@
       "stunserver/stunserver_main.cc",
     ]
     deps = [
-      "../rtc_base:rtc_base",
+      "../base:rtc_base",
+      "//webrtc/base:rtc_base_approved",
       "//webrtc/p2p:rtc_p2p",
       "//webrtc/pc:rtc_pc",
-      "//webrtc/rtc_base:rtc_base_approved",
       "//webrtc/system_wrappers:field_trial_default",
       "//webrtc/system_wrappers:metrics_default",
     ]
@@ -633,13 +633,13 @@
     deps = [
       "//webrtc/api:libjingle_peerconnection_test_api",
       "//webrtc/api:video_frame_api",
+      "//webrtc/base:rtc_base",
+      "//webrtc/base:rtc_base_approved",
+      "//webrtc/base:rtc_json",
       "//webrtc/media:rtc_media",
       "//webrtc/media:rtc_media_base",
       "//webrtc/modules/video_capture:video_capture_module",
       "//webrtc/pc:libjingle_peerconnection",
-      "//webrtc/rtc_base:rtc_base",
-      "//webrtc/rtc_base:rtc_base_approved",
-      "//webrtc/rtc_base:rtc_json",
       "//webrtc/system_wrappers:field_trial_default",
       "//webrtc/system_wrappers:metrics_default",
     ]
@@ -661,10 +661,10 @@
     }
 
     deps = [
+      "../base:rtc_base",
+      "../base:rtc_base_approved",
       "../p2p:libstunprober",
       "../p2p:rtc_p2p",
-      "../rtc_base:rtc_base",
-      "../rtc_base:rtc_base_approved",
       "../system_wrappers:field_trial_default",
     ]
   }