test.py: Push dart_precompiled_runtime and process_test once per device instead of once per test.

tools/testing/dart/android.dart

Index: tools/testing/dart/android.dart
diff --git a/tools/testing/dart/android.dart b/tools/testing/dart/android.dart
index 985f6bc99a7ba67b6313d82698b5f6a753ed5474..423689a9290569fc707c3f795ba48127b747b604 100644
--- a/tools/testing/dart/android.dart
+++ b/tools/testing/dart/android.dart
@@ -193,6 +193,7 @@ class AndroidHelper {
 class AdbDevice {
   static const _adbServerStartupTime = const Duration(seconds: 3);
   String _deviceId;
+  Map<String, String> _cachedData = new Map<String, String>();
 
   String get deviceId => _deviceId;
 
@@ -248,6 +249,19 @@ class AdbDevice {
   }
 
   /**
+   * Upload data to the device, unless [local] is the same as the most recently
+   * used source for [remote].
+   */
+  Future pushCachedData(String local, String remote) {
+    if (_cachedData[remote] == local) {
+      return new Future.value(new AdbCommandResult(
+          "Skipped cached push", "", "", 0, false));
+    }
+    _cachedData[remote] = local;
+    return _adbCommand(['push', local, remote]);
+  }
+
+  /**
    * Change permission of directory recursively.
    */
   Future chmod(String mode, Path directory) {
@@ -416,6 +430,7 @@ class AdbDevicePool {
           'No android devices found. '
           'Please make sure "adb devices" shows your device!');
     }
+    print("Found ${devices.length} Android devices.");
     return new AdbDevicePool(devices);
   }