[SurfaceFlinger] add getDisplayedContentSample i/f

Add interface to ISurfaceComposer that can query the
graphics.composer for statistics on the displayed pixel content.

Bug: 116028618
Test: Boot
Test: ran test client, see data collected
Change-Id: Ide9b81b80c3399e7d648c7b611514e0d699120de
diff --git a/libs/gui/SurfaceComposerClient.cpp b/libs/gui/SurfaceComposerClient.cpp
index 405d228..070b253 100644
--- a/libs/gui/SurfaceComposerClient.cpp
+++ b/libs/gui/SurfaceComposerClient.cpp
@@ -1106,6 +1106,12 @@
                                                                                    maxFrames);
 }
 
+status_t SurfaceComposerClient::getDisplayedContentSample(const sp<IBinder>& display,
+                                                          uint64_t maxFrames, uint64_t timestamp,
+                                                          DisplayedFrameStats* outStats) {
+    return ComposerService::getComposerService()->getDisplayedContentSample(display, maxFrames,
+                                                                            timestamp, outStats);
+}
 // ----------------------------------------------------------------------------
 
 status_t ScreenshotClient::capture(const sp<IBinder>& display, const ui::Dataspace reqDataSpace,