Try all possible Android SDK locations before giving up (#8730)

Fixes #8618

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

@@ -87,8 +87,9 @@ class AndroidSdk {
         return new AndroidSdk(fs.path.join(androidHomeDir, 'sdk'));
     }
 
-    File aaptBin = os.which('aapt'); // in build-tools/$version/aapt
-    if (aaptBin != null) {
+    // in build-tools/$version/aapt
+    final List<File> aaptBins = os.whichAll('aapt');
+    for (File aaptBin in aaptBins) {
       // Make sure we're using the aapt from the SDK.
       aaptBin = fs.file(aaptBin.resolveSymbolicLinksSync());
       final String dir = aaptBin.parent.parent.parent.path;
@@ -96,8 +97,9 @@ class AndroidSdk {
         return new AndroidSdk(dir);
     }
 
-    File adbBin = os.which('adb'); // in platform-tools/adb
-    if (adbBin != null) {
+    // in platform-tools/adb
+    final List<File> adbBins = os.whichAll('adb');
+    for (File adbBin in adbBins) {
       // Make sure we're using the adb from the SDK.
       adbBin = fs.file(adbBin.resolveSymbolicLinksSync());
       final String dir = adbBin.parent.parent.path;

packages/flutter_tools/lib/src/base/os.dart

@@ -5,7 +5,6 @@
 import 'dart:async';
 
 import 'package:archive/archive.dart';
-
 import 'context.dart';
 import 'file_system.dart';
 import 'io.dart';
@@ -34,6 +33,28 @@ abstract class OperatingSystemUtils {
   /// if `which` was not able to locate the binary.
   File which(String execName);
 
+  /// Return a list of all paths to `execName` found on the system. Uses the
+  /// PATH environment variable.
+  List<File> whichAll(String execName) {
+    final List<File> result = <File>[];
+    final String pathEnvironmentVariable = platform.environment['PATH'];
+    for (final String pathComponent in _splitPath(pathEnvironmentVariable)) {
+      final String pathToExecName = fs.path.join(pathComponent, execName);
+      if (processManager.canRun(pathToExecName)) {
+        result.add(fs.file(pathToExecName));
+      }
+    }
+    return result;
+  }
+
+  List<String> _splitPath(String pathEnvironmentVariable) {
+    final String delimiter = platform.isWindows ? ';' : ':';
+    if (pathEnvironmentVariable == null) {
+      return <String>[];
+    }
+    return pathEnvironmentVariable.split(delimiter);
+  }
+
   /// Return the File representing a new pipe.
   File makePipe(String path);
 

packages/flutter_tools/test/src/context.dart

@@ -151,7 +151,10 @@ class MockSimControl extends Mock implements SimControl {
   }
 }
 
-class MockOperatingSystemUtils extends Mock implements OperatingSystemUtils {}
+class MockOperatingSystemUtils extends Mock implements OperatingSystemUtils {
+  @override
+  List<File> whichAll(String execName) => <File>[];
+}
 
 class MockIOSSimulatorUtils extends Mock implements IOSSimulatorUtils {}