Add Fps class

Add a class to wrap a fps value. This is useful because across
the code we
 - convert between vsyncPeriod and fps
 - compare with tolerance (this ensures we use consistent tolerance)
 - consistent toString method

Bug: 159590486
Test: presubmit
Change-Id: Iebb77a33a2f822056642aa61bd6fac6514aa656d
diff --git a/services/surfaceflinger/tests/unittests/FakeVsyncConfiguration.h b/services/surfaceflinger/tests/unittests/FakeVsyncConfiguration.h
index 4cd1e0a..36e24d2 100644
--- a/services/surfaceflinger/tests/unittests/FakeVsyncConfiguration.h
+++ b/services/surfaceflinger/tests/unittests/FakeVsyncConfiguration.h
@@ -26,7 +26,7 @@
     static constexpr nsecs_t FAKE_PHASE_OFFSET_NS = 0;
     static constexpr auto FAKE_DURATION_OFFSET_NS = std::chrono::nanoseconds(0);
 
-    VsyncConfigSet getConfigsForRefreshRate(float) const override { return getCurrentConfigs(); }
+    VsyncConfigSet getConfigsForRefreshRate(Fps) const override { return getCurrentConfigs(); }
 
     VsyncConfigSet getCurrentConfigs() const override {
         return {{FAKE_PHASE_OFFSET_NS, FAKE_PHASE_OFFSET_NS, FAKE_DURATION_OFFSET_NS,
@@ -37,7 +37,7 @@
                  FAKE_DURATION_OFFSET_NS}};
     }
 
-    void setRefreshRateFps(float) override {}
+    void setRefreshRateFps(Fps) override {}
     void dump(std::string&) const override {}
 };