Don't reinstall the app if the latest build is already installed. (#8328)

Only implemented for Android devices for now. Compare the installed SHA1
to the latest build. If they match, there's no reason to reinstall the
build.

Fixes #8295

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

@@ -196,6 +196,10 @@ class AndroidDevice extends Device {
     return '/data/local/tmp/sky.${app.id}.sha1';
   }
 
+  String _getDeviceApkSha1(ApplicationPackage app) {
+    return runSync(adbCommandForDevice(<String>['shell', 'cat', _getDeviceSha1Path(app)]));
+  }
+
   String _getSourceSha1(ApplicationPackage app) {
     AndroidApk apk = app;
     File shaFile = fs.file('${apk.apkPath}.sha1');
@@ -212,6 +216,12 @@ class AndroidDevice extends Device {
     return LineSplitter.split(listOut).contains("package:${app.id}");
   }
 
+  @override
+  bool isLatestBuildInstalled(ApplicationPackage app) {
+    String installedSha1 = _getDeviceApkSha1(app);
+    return installedSha1.isNotEmpty && installedSha1 == _getSourceSha1(app);
+  }
+
   @override
   bool installApp(ApplicationPackage app) {
     AndroidApk apk = app;
@@ -286,16 +296,20 @@ class AndroidDevice extends Device {
       );
     }
 
-    if (isAppInstalled(package)) {
-      printStatus('Uninstalling old version...');
-      if (!uninstallApp(package))
-        printError('Warning: uninstalling old version failed');
-    }
+    if (isLatestBuildInstalled(package)) {
+      printStatus('Latest build already installed.');
+    } else {
+      if (isAppInstalled(package)) {
+        printStatus('Uninstalling old version...');
+        if (!uninstallApp(package))
+          printError('Warning: uninstalling old version failed');
+      }
 
-    printTrace('Installing APK.');
-    if (!installApp(package)) {
-      printTrace('Error: Failed to install APK.');
-      return new LaunchResult.failed();
+      printTrace('Installing APK.');
+      if (!installApp(package)) {
+        printTrace('Error: Failed to install APK.');
+        return new LaunchResult.failed();
+      }
     }
 
     final bool traceStartup = platformArgs['trace-startup'] ?? false;

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

@@ -175,5 +175,10 @@ Future<Null> buildGradleProjectV2(String gradle, String buildModeName) async {
   File apkFile = fs.file('$gradleAppOutDir/$apkFilename');
   // Copy the APK to app.apk, so `flutter run`, `flutter install`, etc. can find it.
   apkFile.copySync('$gradleAppOutDir/app.apk');
+
+  printTrace('calculateSha: $gradleAppOutDir/app.apk');
+  File apkShaFile = fs.file('$gradleAppOutDir/app.apk.sha1');
+  apkShaFile.writeAsStringSync(calculateSha(apkFile));
+
   printStatus('Built $apkFilename (${getSizeAsMB(apkFile.lengthSync())}).');
 }

packages/flutter_tools/lib/src/device.dart

@@ -151,6 +151,9 @@ abstract class Device {
   /// Check if a version of the given app is already installed
   bool isAppInstalled(ApplicationPackage app);
 
+  /// Check if the latest build of the [app] is already installed.
+  bool isLatestBuildInstalled(ApplicationPackage app);
+
   /// Install an app package on the current device
   bool installApp(ApplicationPackage app);
 

packages/flutter_tools/lib/src/ios/devices.dart

@@ -152,6 +152,9 @@ class IOSDevice extends Device {
     return false;
   }
 
+  @override
+  bool isLatestBuildInstalled(ApplicationPackage app) => false;
+
   @override
   bool installApp(ApplicationPackage app) {
     IOSApp iosApp = app;

packages/flutter_tools/lib/src/ios/simulators.dart

@@ -340,6 +340,9 @@ class IOSSimulator extends Device {
     return SimControl.instance.isInstalled(app.id);
   }
 
+  @override
+  bool isLatestBuildInstalled(ApplicationPackage app) => false;
+
   @override
   bool installApp(ApplicationPackage app) {
     try {