Convert //ui to not depend on set_sources_assignment_filter()

set_sources_assignment_filter() is considered as a mis-feature
of gn (as it makes it difficult to reason about the BUILD.gn
files individually).

Convert BUILD.gn files below //ui to instead use conditional
to include source files only on the platformn where they are
used.

The conversion was done by using a modified version of gn that
display all files filtered by set_sources_assignment_filter()
and updating the BUILD.gn files manually to explicitly add the
source files only on the platform that used them.

This CL was uploaded by git cl split.

Bug: 1018739
Change-Id: Ieda60fcfd3fc525d679d29b0f8665004abc8e730
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1929822
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Robert Flack <flackr@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719548}

ui/gfx/animation/BUILD.gn

@@ -5,6 +5,12 @@
 import("//build/config/jumbo.gni")
 import("//build/config/ui.gni")
 
+# Reset sources_assignment_filter for the BUILD.gn file to prevent
+# regression during the migration of Chromium away from the feature.
+# See build/no_sources_assignment_filter.md for more information.
+# TODO(crbug.com/1018739): remove this when migration is done.
+set_sources_assignment_filter([])
+
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
@@ -14,31 +20,38 @@ jumbo_component("animation") {
   sources = [
     "animation.cc",
     "animation.h",
-    "animation_android.cc",
     "animation_container.cc",
     "animation_container.h",
     "animation_container_element.h",
     "animation_container_observer.h",
     "animation_delegate.h",
     "animation_export.h",
-    "animation_mac.mm",
     "animation_runner.cc",
     "animation_runner.h",
-    "animation_win.cc",
     "linear_animation.cc",
     "linear_animation.h",
     "multi_animation.cc",
     "multi_animation.h",
     "slide_animation.cc",
     "slide_animation.h",
-    "throb_animation.cc",
-    "throb_animation.h",
     "tween.cc",
     "tween.h",
   ]
 
   if (is_android) {
-    sources -= [
+    sources += [ "animation_android.cc" ]
+  }
+
+  if (is_mac) {
+    sources += [ "animation_mac.mm" ]
+  }
+
+  if (is_win) {
+    sources += [ "animation_win.cc" ]
+  }
+
+  if (!is_android) {
+    sources += [
       "throb_animation.cc",
       "throb_animation.h",
     ]