[SurfaceFlinger] add setDisplayContentSamplingEnabled i/f

Add interface to ISurfaceComposer that can enable or disable
the graphics.composer's collection of the displayed content
statistics.

Bug: 116028618
Test: Boot
Test: ran test client against prototype, see enable/disable working.
Test: Ran new tests './libgui_test --gtest_filter="DisplayedContentSamp*"'
Test: on hwc with and without new function hook.
Change-Id: Ifb487e2bfbd8e0db6178ccbf762aa968c34576b9
diff --git a/services/surfaceflinger/DisplayHardware/HWC2.cpp b/services/surfaceflinger/DisplayHardware/HWC2.cpp
index 2df2d3b..733a5da 100644
--- a/services/surfaceflinger/DisplayHardware/HWC2.cpp
+++ b/services/surfaceflinger/DisplayHardware/HWC2.cpp
@@ -555,6 +555,13 @@
     return static_cast<Error>(intError);
 }
 
+Error Display::setDisplayContentSamplingEnabled(bool enabled, uint8_t componentMask,
+                                                uint64_t maxFrames) const {
+    auto intError =
+            mComposer.setDisplayContentSamplingEnabled(mId, enabled, componentMask, maxFrames);
+    return static_cast<Error>(intError);
+}
+
 Error Display::getReleaseFences(
         std::unordered_map<Layer*, sp<Fence>>* outFences) const
 {