Android: Disable incremental dexing for prebuilts

Small build speed improvement.

Bug: 937005, 1016846
Change-Id: I126ec5fbd3652f843bfb56b185cae8209bf6fe7e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1874186Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Commit-Queue: Eric Stevenson <estevenson@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708300}

build/android/gyp/dex.py

@@ -408,8 +408,10 @@ def main(args):
     final_dex_inputs = _IntermediateDexFilePathsFromInputJars(
         options.class_inputs, options.incremental_dir)
     output_paths += final_dex_inputs
+    track_subpaths_whitelist = options.class_inputs
   else:
     final_dex_inputs = list(options.class_inputs)
+    track_subpaths_whitelist = None
   final_dex_inputs += options.dex_inputs
 
   dex_cmd = [
@@ -429,7 +431,7 @@ def main(args):
       input_paths=input_paths,
       input_strings=dex_cmd + [bool(options.incremental_dir)],
       pass_changes=True,
-      track_subpaths_whitelist=options.class_inputs)
+      track_subpaths_whitelist=track_subpaths_whitelist)
 
 
 if __name__ == '__main__':

build/config/android/internal_rules.gni

@@ -1149,6 +1149,7 @@ if (enable_java_templates) {
 
   # Variables
   #   apply_mapping: The path to the ProGuard mapping file to apply.
+  #   disable_incremental: Disable incremental dexing.
   template("dex") {
     assert(defined(invoker.output))
 
@@ -1376,7 +1377,9 @@ if (enable_java_templates) {
 
         if (_proguard_enabled) {
           deps += [ ":${_proguard_target_name}" ]
-        } else if (enable_incremental_d8) {
+        } else if (enable_incremental_d8 &&
+                   !(defined(invoker.disable_incremental) &&
+                     invoker.disable_incremental)) {
           # Don't use incremental dexing for ProGuarded inputs as a precaution.
           args += [
             "--incremental-dir",
@@ -3500,6 +3503,10 @@ if (enable_java_templates) {
         if (defined(_dex_path)) {
           dex("${target_name}__dex") {
             input_class_jars = [ _final_jar_path ]
+
+            # There's no value in per-class dexing prebuilts since they never
+            # change just one class at a time.
+            disable_incremental = _is_prebuilt
             output = _dex_path
             deps = [
               ":$_process_prebuilt_target_name",