Move enable_webrtc to a buildflag header.

chrome/browser/chrome_content_browser_client.h

Index: chrome/browser/chrome_content_browser_client.h
diff --git a/chrome/browser/chrome_content_browser_client.h b/chrome/browser/chrome_content_browser_client.h
index 3d8bb0a1ae8448cf05652b33eeda542d84f5fe8d..a9654ee96ada89f8e593ef5bfa97f11f82a503d8 100644
--- a/chrome/browser/chrome_content_browser_client.h
+++ b/chrome/browser/chrome_content_browser_client.h
@@ -160,11 +160,11 @@ class ChromeContentBrowserClient : public content::ContentBrowserClient {
       const base::string16& name,
       content::ResourceContext* context,
       const std::vector<std::pair<int, int>>& render_frames) override;
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
   bool AllowWebRTCIdentityCache(const GURL& url,
                                 const GURL& first_party_url,
                                 content::ResourceContext* context) override;
-#endif  // defined(ENABLE_WEBRTC)
+#endif  // BUILDFLAG(ENABLE_WEBRTC)
   bool AllowKeygen(const GURL& url, content::ResourceContext* context) override;
   AllowWebBluetoothResult AllowWebBluetooth(
       content::BrowserContext* browser_context,
@@ -323,7 +323,7 @@ class ChromeContentBrowserClient : public content::ContentBrowserClient {
  private:
   friend class DisableWebRtcEncryptionFlagTest;
 
-#if defined(ENABLE_WEBRTC)
+#if BUILDFLAG(ENABLE_WEBRTC)
   // Copies disable WebRTC encryption switch depending on the channel.
   static void MaybeCopyDisableWebRtcEncryptionSwitch(
       base::CommandLine* to_command_line,