Monitor system-wide disk writes and trigger alert on overuse.

Update IoOveruseMonitor to monitor system-wide disk writes and trigger
alert on reaching/exceeding I/O overuse threshold.

Test: Tested with unit tests.
Bug: 167240592

Change-Id: Iafc729ff0e822e4f8524df647cb6ae00969a8bd7
diff --git a/cpp/watchdog/server/Android.bp b/cpp/watchdog/server/Android.bp
index 56f19ee..2afee42 100644
--- a/cpp/watchdog/server/Android.bp
+++ b/cpp/watchdog/server/Android.bp
@@ -105,6 +105,7 @@
     test_suites: ["general-tests"],
     srcs: [
         "tests/IoOveruseConfigsTest.cpp",
+        "tests/IoOveruseMonitorTest.cpp",
         "tests/IoPerfCollectionTest.cpp",
         "tests/LooperStub.cpp",
         "tests/PackageInfoResolverTest.cpp",