Remove DEFINE_WEB_CONTENTS_USER_DATA_KEY in //chromecast.

It is no longer necessary to invoke the DEFINE_WEB_CONTENTS_USER_DATA_KEY
macro to define the global variable from which the key of a
WebContentsUserData is derived. The key is now derived from a static
local variable in WebContentsUserData::UserDataKey().
See https://chromium-review.googlesource.com/c/chromium/src/+/1093015

This CL was uploaded by git cl split.

R=slan@chromium.org

Bug: 589840
Change-Id: I9742e8415f6b34bad58acba7ccdc50e4d5ddf12e
Reviewed-on: https://chromium-review.googlesource.com/1150282Reviewed-by: Stephen Lanham <slan@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581215}

chromecast/browser/extensions/api/automation_internal/automation_internal_api.cc

@@ -51,9 +51,6 @@ class AutomationWebContentsObserver;
 }  // namespace cast
 }  // namespace extensions
 
-DEFINE_WEB_CONTENTS_USER_DATA_KEY(
-    extensions::cast::AutomationWebContentsObserver);
-
 namespace extensions {
 namespace cast {
 

chromecast/browser/extensions/cast_extension_web_contents_observer.cc

@@ -4,8 +4,6 @@
 
 #include "chromecast/browser/extensions/cast_extension_web_contents_observer.h"
 
-DEFINE_WEB_CONTENTS_USER_DATA_KEY(extensions::CastExtensionWebContentsObserver);
-
 namespace extensions {
 
 CastExtensionWebContentsObserver::CastExtensionWebContentsObserver(