[AW][Dev-UI] autogenerate AwFeatures

No change to logic. This autogenerates AwFeatures.java from
aw_features.cc using the java_cpp_features GN rule.

Fixed: 1128789
Test: autoninja -C out/Default system_webview_apk
Change-Id: If3f3f36384e04328428f3feb05bffa62c02fcdf8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2412798
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812934}

android_webview/BUILD.gn

@@ -632,9 +632,15 @@ java_cpp_strings("common_java_switches_srcjar") {
   template = "java/src/org/chromium/android_webview/common/AwSwitches.java.tmpl"
 }
 
+java_cpp_features("common_java_features_srcjar") {
+  # External code should depend on "common_java" instead.
+  visibility = [ ":*" ]
+  sources = [ "common/aw_features.cc" ]
+  template = "java/src/org/chromium/android_webview/common/AwFeatures.java.tmpl"
+}
+
 android_library("common_java") {
   sources = [
-    "java/src/org/chromium/android_webview/common/AwFeatures.java",
     "java/src/org/chromium/android_webview/common/AwResource.java",
     "java/src/org/chromium/android_webview/common/CommandLineUtil.java",
     "java/src/org/chromium/android_webview/common/DeveloperModeUtils.java",
@@ -650,7 +656,10 @@ android_library("common_java") {
     "//gpu/config:config_java",
     "//third_party/android_deps:androidx_annotation_annotation_java",
   ]
-  srcjar_deps = [ ":common_java_switches_srcjar" ]
+  srcjar_deps = [
+    ":common_java_features_srcjar",
+    ":common_java_switches_srcjar",
+  ]
 }
 
 android_aidl("common_aidl") {

android_webview/docs/commandline-flags.md

@@ -146,9 +146,11 @@ WebView also defines its own flags and Features:
    [`java_cpp_strings`](/docs/android_accessing_cpp_switches_in_java.md) to
    automatically generate Java switch constants from the C++ switches (see
    [`AwSwitches.java`](https://source.chromium.org/chromium/chromium/src/+/master:out/android-Debug/gen/android_webview/common_java/generated_java/input_srcjars/org/chromium/android_webview/common/AwSwitches.java)).
- * [AwFeatureList.java](https://cs.chromium.org/chromium/src/android_webview/java/src/org/chromium/android_webview/AwFeatureList.java)
-   (and its [native
-   counterpart](https://cs.chromium.org/chromium/src/android_webview/common/aw_features.h))
+ * C++ `base::Features` are defined in
+   [`aw_features.cc`](/android_webview/common/aw_features.cc). We use
+   [`java_cpp_features`](/docs/android_accessing_cpp_features_in_java.md) to
+   automatically generate Java constants from the C++ Features (see
+   [`AwFeatures.java`](https://source.chromium.org/chromium/chromium/src/+/master:out/android-Debug/gen/android_webview/common_java/generated_java/input_srcjars/org/chromium/android_webview/common/AwFeatures.java)).
 
 ## Implementation
 

android_webview/java/src/org/chromium/android_webview/common/AwFeatures.java

-// 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.
-
-package org.chromium.android_webview.common;
-
-/**
- * Constants for the names of WebView Features.
- *
- * These must match the names in aw_features.cc.
- */
-public final class AwFeatures {
-    // Alphabetical:
-    public static final String WEBVIEW_CONNECTIONLESS_SAFE_BROWSING =
-            "WebViewConnectionlessSafeBrowsing";
-
-    public static final String WEBVIEW_DISPLAY_CUTOUT = "WebViewDisplayCutout";
-
-    public static final String WEBVIEW_EXTRA_HEADERS_SAME_DOMAIN_ONLY =
-            "WebViewExtraHeadersSameDomainOnly";
-
-    public static final String WEBVIEW_EXTRA_HEADERS_SAME_ORIGIN_ONLY =
-            "WebViewExtraHeadersSameOriginOnly";
-
-    public static final String WEBVIEW_TEST_FEATURE = "WebViewTestFeature";
-
-    private AwFeatures() {}
-}

android_webview/java/src/org/chromium/android_webview/common/AwFeatures.java.tmpl

+// 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.
+
+package org.chromium.android_webview.common;
+
+/**
+ * Constants for the names of WebView Features.
+ */
+public final class AwFeatures {{
+
+{NATIVE_FEATURES}
+
+    // Do not instantiate this class.
+    private AwFeatures() {{}}
+}}

android_webview/java/src/org/chromium/android_webview/common/ProductionSupportedFlagList.java

@@ -69,8 +69,8 @@ public final class ProductionSupportedFlagList {
             Flag.baseFeature(AwFeatures.WEBVIEW_CONNECTIONLESS_SAFE_BROWSING,
                     "Uses GooglePlayService's 'connectionless' APIs for Safe Browsing "
                             + "security checks."),
-            Flag.baseFeature(
-                    "WebViewBrotliSupport", "Enables brotli compression support in WebView."),
+            Flag.baseFeature(AwFeatures.WEBVIEW_BROTLI_SUPPORT,
+                    "Enables brotli compression support in WebView."),
             Flag.baseFeature(
                     "AppCache", "Controls AppCache to facilitate testing against future removal."),
             Flag.baseFeature(AwFeatures.WEBVIEW_EXTRA_HEADERS_SAME_ORIGIN_ONLY,