[flutter_tools] include depfile outputs in gradle outputs (#50877)

packages/flutter_tools/gradle/flutter.gradle

@@ -891,13 +891,13 @@ class FlutterTask extends BaseFlutterTask {
         }
     }
 
-    FileCollection readDependencies(File dependenciesFile) {
+    FileCollection readDependencies(File dependenciesFile, Boolean inputs) {
       if (dependenciesFile.exists()) {
         // Dependencies file has Makefile syntax:
         //   <target> <files>: <source> <files> <separated> <by> <non-escaped space>
         String depText = dependenciesFile.text
         // So we split list of files by non-escaped(by backslash) space,
-        def matcher = depText.split(': ')[1] =~ /(\\ |[^\s])+/
+        def matcher = depText.split(': ')[inputs ? 1 : 0] =~ /(\\ |[^\s])+/
         // then we replace all escaped spaces with regular spaces
         def depList = matcher.collect{it[0].replaceAll("\\\\ ", " ")}
         return project.files(depList)
@@ -909,11 +909,20 @@ class FlutterTask extends BaseFlutterTask {
     FileCollection getSourceFiles() {
         FileCollection sources = project.files()
         for (File depfile in getDependenciesFiles()) {
-          sources += readDependencies(depfile)
+          sources += readDependencies(depfile, true)
         }
         return sources + project.files('pubspec.yaml')
     }
 
+    @OutputFiles
+    FileCollection getOutputFiles() {
+        FileCollection sources = project.files()
+        for (File depfile in getDependenciesFiles()) {
+          sources += readDependencies(depfile, false)
+        }
+        return sources
+    }
+
     @TaskAction
     void build() {
         buildBundle()