android build: Split process_resources GN rule and script.

The process_resources() GN template and the associated
process_resources.py script are huge and difficult to understand
because they can be used to perform two slightly related
different things.

In preparation for a future CL that will introduce a new resource
compilation mode, this CL tries to clarify the situation by splitting
them into two sets of GN template + script:

   - prepare_resources() + prepare_resources.py, which are
     used to create .resources.zip archives of raw/uncompiled
     resources for resource related targets, as well as
     generating a corresponding R.txt and .srcjar(R.java)
     file.

     This corresponds to what process_resources() did when
     it was called from android_resources() and junit_binary().

     Note that this always generates non-final resource IDs,
     as well as a dummy onResourcesLoaded() method, necessary
     to compile, but not link, the ResourceRewriter class
     used to implement the system webview feature.

   - compile_resources() + compile_resources.py, which are used
     to compile all resource dependencies of a given binary
     (e.g. android_apk) into an intermediate .ap_ file.

     This corresponds to the behaviour of process_resources()
     when called from android_apk(). This generates final
     resource IDs by default, unless |shared_resources| or
     |shared_resources_whitelist| is used.

     Also, as a simplification, |shared_resources_whitelist|
     now implies |shared_resources|, except that it restrict
     the list of non-final resource IDs.

- Removed generate_constant_ids, since compile_resources()
  will always generate constant ids unless shared resources
  are being used. And prepare_resources() always generates
  non-constant IDs, as before the CL.

+ Add documentation for the prepare_resources() and
  compile_resources() internal GN rules, to make them
  a little less intimidating.

+ Removed |app_as_shared_lib|, since even before this CL all
  resources were generated with package ID 0x7f anyway, or
  fixed a compile_resources() time. Hence |shared_resources|
  did the exact same thing.

+ Improve --help output for prepare_resources.py and
  compile_resources.py by using option groups for inputs
  and outputs.

R=agrieve@chromium.org,yfriedman@chromium.org,estevenson@chromium.org,trevordixon@chromium.org

Bug: 820459
Change-Id: If05ac24a57c4dfa11f9ce43c30ab22e957b2765d
Reviewed-on: https://chromium-review.googlesource.com/957095
Commit-Queue: David Turner <digit@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543957}

build/config/android/rules.gni

@@ -723,8 +723,6 @@ if (enable_java_templates) {
   #     false. (see build/android/gyp/generate_v14_compatible_resources.py)
   #   shared_resources: If true make a resource package that can be loaded by a
   #     different application at runtime to access the package's resources.
-  #   app_as_shared_lib: If true make a resource package that can be loaded as
-  #     both shared_resources and normal application.
   #   r_text_file: (optional) path to pre-generated R.txt to be used when
   #     generating R.java instead of resource-based aapt-generated one.
   #   create_srcjar: If false, does not create an R.java file. Needed only for
@@ -792,17 +790,15 @@ if (enable_java_templates) {
       }
     }
 
-    process_resources(target_name) {
+    prepare_resources(target_name) {
       forward_variables_from(invoker,
                              [
-                               "app_as_shared_lib",
                                "android_manifest",
                                "custom_package",
                                "deps",
                                "generated_resource_dirs",
                                "generated_resource_files",
                                "resource_dirs",
-                               "shared_resources",
                                "v14_skip",
                              ])
       if (!defined(deps)) {
@@ -1151,8 +1147,8 @@ if (enable_java_templates) {
       _deps += invoker.deps
     }
 
-    _process_resources_target = "${target_name}__process_resources"
-    process_resources(_process_resources_target) {
+    _prepare_resources_target = "${target_name}__prepare_resources"
+    prepare_resources(_prepare_resources_target) {
       deps = _deps + [ ":$_build_config_target_name" ]
       build_config = _build_config
       srcjar_path = "${target_gen_dir}/${target_name}.srcjar"
@@ -1182,7 +1178,7 @@ if (enable_java_templates) {
         srcjar_deps = []
       }
       srcjar_deps += [
-        ":$_process_resources_target",
+        ":$_prepare_resources_target",
 
         # This dep is required for any targets that depend on //base:base_java.
         "//base:base_build_config_gen",
@@ -2014,12 +2010,11 @@ if (enable_java_templates) {
           "$_base_path.resources.main-dex-proguard.txt"
     }
     _generated_proguard_config = "$_base_path.resources.proguard.txt"
-    _process_resources_target = "${_template_name}__process_resources"
-    process_resources(_process_resources_target) {
+    _compile_resources_target = "${_template_name}__compile_resources"
+    compile_resources(_compile_resources_target) {
       forward_variables_from(invoker,
                              [
                                "alternative_android_sdk_jar",
-                               "app_as_shared_lib",
                                "shared_resources",
                                "support_zh_hk",
                                "aapt_locale_whitelist",
@@ -2036,7 +2031,6 @@ if (enable_java_templates) {
       }
       srcjar_path = "${target_gen_dir}/${target_name}.srcjar"
       r_text_out_path = "${target_gen_dir}/${target_name}_R.txt"
-      generate_constant_ids = true
       proguard_file = _generated_proguard_config
       if (_enable_multidex) {
         proguard_file_main_dex = _generated_proguard_main_dex_config
@@ -2056,13 +2050,13 @@ if (enable_java_templates) {
             get_label_info(invoker.shared_resources_whitelist_target, "name")
         shared_resources_whitelist =
             "${_whitelist_gen_dir}/${_whitelist_target_name}" +
-            "__process_resources_R.txt"
+            "__compile_resources_R.txt"
         deps += [
-          "${invoker.shared_resources_whitelist_target}__process_resources",
+          "${invoker.shared_resources_whitelist_target}__compile_resources",
         ]
       }
     }
-    _srcjar_deps += [ ":$_process_resources_target" ]
+    _srcjar_deps += [ ":$_compile_resources_target" ]
 
     if (_native_libs_deps != []) {
       _enable_chromium_linker_tests = false
@@ -2240,7 +2234,7 @@ if (enable_java_templates) {
                                ])
         deps = _deps + [
                  ":$_build_config_target",
-                 ":$_process_resources_target",
+                 ":$_compile_resources_target",
                  ":$_java_target",
                ]
         inputs = [
@@ -2298,7 +2292,7 @@ if (enable_java_templates) {
 
       if (_enable_multidex) {
         extra_main_dex_proguard_config = _generated_proguard_main_dex_config
-        deps += [ ":$_process_resources_target" ]
+        deps += [ ":$_compile_resources_target" ]
       }
 
       # All deps are already included in _dex_sources when proguard is used.
@@ -2426,7 +2420,7 @@ if (enable_java_templates) {
       incremental_deps = _deps + [
                            ":$_merge_manifest_target",
                            ":$_build_config_target",
-                           ":$_process_resources_target",
+                           ":$_compile_resources_target",
                          ]
 
       # This target generates the input file _all_resources_zip_path.
@@ -2434,7 +2428,7 @@ if (enable_java_templates) {
                ":$_merge_manifest_target",
                ":$_build_config_target",
                ":$_final_dex_target_name",
-               ":$_process_resources_target",
+               ":$_compile_resources_target",
              ]
 
       if (_native_libs_deps != [] ||

chrome/android/chrome_public_apk_tmpl.gni

@@ -112,7 +112,6 @@ template("monochrome_public_apk_tmpl") {
     }
 
     alternative_android_sdk_jar = webview_framework_jar
-    app_as_shared_lib = true
     use_chromium_linker = false
     requires_sdk_api_level_23 = true