mac: Convert GN libs lists to frameworks in //content.

GN recently added support for Apple frameworks to link, rather than
overloading the libs lists. This pulls .frameworks out of the libs
lists, so that GN can stop supporting .frameworks in libs in the
future.

Bug: 1052560
Change-Id: I3292ad8d76e9b25e56f01f52db8c3fc9aedf3a76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2276660
Auto-Submit: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784311}

content/test/BUILD.gn

@@ -2307,7 +2307,7 @@ test("content_unittests") {
       "//ui/accelerated_widget_mac",
       "//ui/base/mojom",
     ]
-    libs = [
+    frameworks = [
       "Carbon.framework",
       "IOSurface.framework",
     ]