[AW] Move //aw/gpu/ into its own build file

Bug: 934152
Test: gn check out/Default //android_webview/gpu
Change-Id: I083a3fd762b7b0c8a819db8e0dc09261cd6662fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1764339Reviewed-by: Changwan Ryu <changwan@chromium.org>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Commit-Queue: Robbie McElrath <rmcelrath@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689556}

android_webview/BUILD.gn

@@ -649,8 +649,6 @@ source_set("common") {
     "browser/tracing/aw_tracing_controller.h",
     "browser/tracing/aw_tracing_delegate.cc",
     "browser/tracing/aw_tracing_delegate.h",
-    "gpu/aw_content_gpu_client.cc",
-    "gpu/aw_content_gpu_client.h",
     "lib/aw_main_delegate.cc",
     "lib/aw_main_delegate.h",
     "lib/webview_jni_onload.cc",
@@ -696,6 +694,7 @@ source_set("common") {
     "//android_webview/browser/gfx:gfx",
     "//android_webview/common",
     "//android_webview/common:common_mojom",
+    "//android_webview/gpu",
     "//base/third_party/dynamic_annotations:dynamic_annotations",
     "//components/about_ui",
     "//components/autofill/android:provider",

android_webview/gpu/BUILD.gn

+# Copyright 2019 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+source_set("gpu") {
+  sources = [
+    "aw_content_gpu_client.cc",
+    "aw_content_gpu_client.h",
+  ]
+
+  deps = [
+    "//base",
+    "//content/public/gpu",
+  ]
+}