SF: rate-limit luma sampling

Instead of sampling the luma regions every frame, introduce a rate
limiting system to reduce load. Introduces a few tunables to control
the rate, which is defaulted to 10Hz, when there is content being
watched for luma.

Test: manual systrace inspection, using SamplingDemo
Test: libgui_test --gtest_filter="RegionSampling*"
Test: atest CompositionSamplingListenerTest
Fixes: 126747045
Change-Id: I7cae3e90fb405ba72dc2f276a88be48f1533a219
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index dba1f8e..08a9eeb 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -637,6 +637,10 @@
     mVsyncModulator.setSchedulerAndHandles(mScheduler.get(), mAppConnectionHandle.get(),
                                            mSfConnectionHandle.get());
 
+    mRegionSamplingThread =
+            new RegionSamplingThread(*this, *mScheduler,
+                                     RegionSamplingThread::EnvironmentTimingTunables());
+
     // Get a RenderEngine for the given display / config (can't fail)
     int32_t renderEngineFeature = 0;
     renderEngineFeature |= (useColorManagement ?
@@ -2063,8 +2067,8 @@
     mTransactionCompletedThread.addPresentFence(mPreviousPresentFence);
     mTransactionCompletedThread.sendCallbacks();
 
-    if (mLumaSampling) {
-        mRegionSamplingThread->sampleNow();
+    if (mLumaSampling && mRegionSamplingThread) {
+        mRegionSamplingThread->notifyNewContent();
     }
 }