Weak link MediaPlayer.framework in //ui/base/now_playing.

This framework is only available on 10.12+, and the normal framework
dependency is causing Chrome on macOS 10.10 and 10.11 to crash on
launch.

Bug: 943299
Change-Id: Ida122e7b339835ac67f20c25880e2e74c4f878b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1529924Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641979}

ui/base/now_playing/BUILD.gn

@@ -2,6 +2,15 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+config("media_player_weak_link") {
+  ldflags = [
+    "-weak_framework",
+    "MediaPlayer",
+  ]
+
+  visibility = [ ":now_playing" ]
+}
+
 component("now_playing") {
   sources = [
     "now_playing_info_center_delegate.cc",
@@ -26,10 +35,13 @@ component("now_playing") {
     "//base",
   ]
 
-  libs = [
-    "Foundation.framework",
-    "MediaPlayer.framework",
-  ]
+  libs = [ "Foundation.framework" ]
+
+  # MediaPlayer.framework is only available on macOS 10.12 and higher. In a
+  # release build, component() is a static_library, which does not transitively
+  # carry weak_link information. Ensure that all targets that directly or
+  # indirectly carry the weak_link on the framework.
+  all_dependent_configs = [ ":media_player_weak_link" ]
 }
 
 static_library("test_support") {