Add frame rate flexibility token

Add support for temporarily relaxing frame rate restrictions in surface
flinger. This is used by CTS tests to get a consistent device state
while running frame rate tests.

Bug: 148033900

Test: - On a Pixel 4, I turned the brightness down and covered the
ambient light sensor, causing the display manager to set a frame rate
restriction. I ran the frame rate CTS test without these CLs applied,
and confirmed the test failed because surface flinger couldn't switch
frame rates, as expected. Then I ran the tests with the CLs applied, and
confirmed the tests pass.

- I confirmed that, without adopting shell permission identity, the CTS
test is denied the request to acquire a frame rate flexibility token. So
normal apps won't be able to access this.

Change-Id: I6685edc4bc07c7888b79a9dd72a90f56b74e7604
diff --git a/libs/gui/tests/Surface_test.cpp b/libs/gui/tests/Surface_test.cpp
index 8c0f8f8..ef1fd02 100644
--- a/libs/gui/tests/Surface_test.cpp
+++ b/libs/gui/tests/Surface_test.cpp
@@ -859,6 +859,8 @@
         return NO_ERROR;
     }
 
+    status_t acquireFrameRateFlexibilityToken(sp<IBinder>* /*outToken*/) { return NO_ERROR; }
+
 protected:
     IBinder* onAsBinder() override { return nullptr; }