Add a re-parent function to re-parent a specific child.

This is similar to reparentChildren, but the reparentChild will
only re-parent a specific child to the new parent and not all
children.

Test: Added test in Transaction_test for reparentChild.

Change-Id: I4275e0d5f1d5601b489956753c78a56d1a5d4c1c
diff --git a/services/surfaceflinger/tests/Transaction_test.cpp b/services/surfaceflinger/tests/Transaction_test.cpp
index 4ce14f8..aef5a5f 100644
--- a/services/surfaceflinger/tests/Transaction_test.cpp
+++ b/services/surfaceflinger/tests/Transaction_test.cpp
@@ -1123,4 +1123,33 @@
     fillSurfaceRGBA8(mFGSurfaceControl, 0, 255, 0);
 }
 
+TEST_F(ChildLayerTest, ReparentChild) {
+    SurfaceComposerClient::openGlobalTransaction();
+    mChild->show();
+    mChild->setPosition(10, 10);
+    mFGSurfaceControl->setPosition(64, 64);
+    SurfaceComposerClient::closeGlobalTransaction(true);
+
+    {
+        ScreenCapture::captureScreen(&mCapture);
+        // Top left of foreground must now be visible
+        mCapture->expectFGColor(64, 64);
+        // But 10 pixels in we should see the child surface
+        mCapture->expectChildColor(74, 74);
+        // And 10 more pixels we should be back to the foreground surface
+        mCapture->expectFGColor(84, 84);
+    }
+    mFGSurfaceControl->reparentChild(mBGSurfaceControl->getHandle(), mChild->getHandle());
+    {
+        ScreenCapture::captureScreen(&mCapture);
+        mCapture->expectFGColor(64, 64);
+        // In reparenting we should have exposed the entire foreground surface.
+        mCapture->expectFGColor(74, 74);
+        // And the child layer should now begin at 10, 10 (since the BG
+        // layer is at (0, 0)).
+        mCapture->expectBGColor(9, 9);
+        mCapture->expectChildColor(10, 10);
+    }
+}
+
 }