Fix local engine support for Gradle builds. (#8362)

Fixes #6761.

packages/flutter_tools/gradle/flutter.gradle

@@ -31,6 +31,7 @@ class FlutterPlugin implements Plugin<Project> {
     private File flutterRoot
     private File flutterExecutable
     private String localEngine
+    private String localEngineSrcPath
     private Properties localProperties
 
     private String resolveProperty(Project project, String name, String defaultValue) {
@@ -41,7 +42,7 @@ class FlutterPlugin implements Plugin<Project> {
                 localProperties.load(localPropertiesFile.newDataInputStream())
             }
         }
-        String result;
+        String result
         if (project.hasProperty(name)) {
             result = project.property(name)
         }
@@ -75,12 +76,20 @@ class FlutterPlugin implements Plugin<Project> {
         String flutterExecutableName = Os.isFamily(Os.FAMILY_WINDOWS) ? "flutter.bat" : "flutter"
         flutterExecutable = Paths.get(flutterRoot.absolutePath, "bin", flutterExecutableName).toFile();
 
-        String flutterJarPath = localProperties.getProperty("flutter.jar")
-        if (flutterJarPath != null) {
-            File flutterJar = project.file(flutterJarPath)
+        if (project.hasProperty('localEngineOut')) {
+            String engineOutPath = project.property('localEngineOut')
+            File engineOut = project.file(engineOutPath)
+            if (!engineOut.isDirectory()) {
+                throw new GradleException('localEngineOut must point to a local engine build')
+            }
+            File flutterJar = Paths.get(engineOut.absolutePath, "flutter.jar").toFile()
             if (!flutterJar.isFile()) {
-                throw new GradleException("flutter.jar must point to a Flutter engine JAR")
+                throw new GradleException('Local engine build does not contain flutter.jar')
             }
+
+            localEngine = engineOut.name
+            localEngineSrcPath = engineOut.parentFile.parent
+
             project.dependencies {
                 compile project.files(flutterJar)
             }
@@ -119,8 +128,6 @@ class FlutterPlugin implements Plugin<Project> {
             }
         }
 
-        localEngine = localProperties.getProperty("flutter.localEngine")
-
         project.extensions.create("flutter", FlutterExtension)
         project.afterEvaluate this.&addFlutterTask
     }
@@ -135,7 +142,9 @@ class FlutterPlugin implements Plugin<Project> {
             target = 'lib/main.dart'
         }
 
-        project.compileDebugJavaWithJavac.dependsOn project.flutterBuildX86Jar
+        if (project.tasks.findByName('flutterBuildX86Jar')) {
+            project.compileDebugJavaWithJavac.dependsOn project.flutterBuildX86Jar
+        }
 
         project.android.applicationVariants.all { variant ->
             if (!["debug", "profile", "release"].contains(variant.name)) {
@@ -147,6 +156,7 @@ class FlutterPlugin implements Plugin<Project> {
                 flutterExecutable this.flutterExecutable
                 buildMode variant.name
                 localEngine this.localEngine
+                localEngineSrcPath this.localEngineSrcPath
                 targetPath target
                 sourceDir project.file(project.flutter.source)
                 intermediateDir project.file("${project.buildDir}/${AndroidProject.FD_INTERMEDIATES}/flutter/${variant.name}")
@@ -173,6 +183,7 @@ class FlutterTask extends DefaultTask {
     File flutterExecutable
     String buildMode
     String localEngine
+    String localEngineSrcPath
     String targetPath
 
     File sourceDir
@@ -211,6 +222,7 @@ class FlutterTask extends DefaultTask {
                 workingDir sourceDir
                 if (localEngine != null) {
                     args "--local-engine", localEngine
+                    args "--local-engine-src-path", localEngineSrcPath
                 }
                 args "build", "aot"
                 args "--target", targetPath
@@ -225,6 +237,7 @@ class FlutterTask extends DefaultTask {
             workingDir sourceDir
             if (localEngine != null) {
                 args "--local-engine", localEngine
+                args "--local-engine-src-path", localEngineSrcPath
             }
             args "build", "flx"
             args "--target", targetPath

packages/flutter_tools/lib/src/android/gradle.dart

@@ -11,6 +11,7 @@ import '../base/os.dart';
 import '../base/platform.dart';
 import '../base/process.dart';
 import '../base/utils.dart';
+import '../artifacts.dart';
 import '../build_info.dart';
 import '../cache.dart';
 import '../globals.dart';
@@ -158,9 +159,16 @@ Future<Null> buildGradleProjectV2(String gradle, String buildModeName) async {
   // Run 'gradle assemble<BuildMode>'.
   Status status = logger.startProgress('Running \'gradle $assembleTask\'...', expectSlowOperation: true);
   String gradlePath = fs.file(gradle).absolute.path;
-  List<String> command = logger.isVerbose
-      ? <String>[gradlePath, assembleTask]
-      : <String>[gradlePath, '-q', assembleTask];
+  List<String> command = <String>[gradlePath];
+  if (!logger.isVerbose) {
+    command.add('-q');
+  }
+  if (artifacts is LocalEngineArtifacts) {
+    LocalEngineArtifacts localEngineArtifacts = artifacts;
+    printTrace('Using local engine: ${localEngineArtifacts.engineOutPath}');
+    command.add('-PlocalEngineOut=${localEngineArtifacts.engineOutPath}');
+  }
+  command.add(assembleTask);
   int exitcode = await runCommandAndStreamOutput(
       command,
       workingDirectory: 'android',