GetContentTask should catch exceptions and wrap them into AnalysisExceptions.

pkg/analyzer/test/src/task/general_test.dart

Index: pkg/analyzer/test/src/task/general_test.dart
diff --git a/pkg/analyzer/test/src/task/general_test.dart b/pkg/analyzer/test/src/task/general_test.dart
index 664a2d62b9a1c9ccff5b05b0dbd9ee955022559f..a043c84242bc7872ec0911a4c7277869ada7dd8b 100644
--- a/pkg/analyzer/test/src/task/general_test.dart
+++ b/pkg/analyzer/test/src/task/general_test.dart
@@ -66,6 +66,16 @@ class GetContentTaskTest extends EngineTestCase {
     expect(task.outputs[CONTENT], 'foo');
     expect(task.outputs[MODIFICATION_TIME], 42);
   }
+
+  void test_perform_exception() {
+    AnalysisContext context = new _MockContext();
+    Source target = new TestSource();
+    GetContentTask task = new GetContentTask(context, target);
+    when(context.getContents(target)).thenThrow('My exception!');
+    task.perform();
+    expect(task.caughtException, isNotNull);
+    expect(task.outputs, isEmpty);
+  }
 }
 
 class _MockContext extends TypedMock implements AnalysisContext {