Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: Ibdd6a210bb7ff228e3624cc319169f77aca3b51e
diff --git a/core/jni/android_hardware_camera2_legacy_PerfMeasurement.cpp b/core/jni/android_hardware_camera2_legacy_PerfMeasurement.cpp
index f042058..a081665 100644
--- a/core/jni/android_hardware_camera2_legacy_PerfMeasurement.cpp
+++ b/core/jni/android_hardware_camera2_legacy_PerfMeasurement.cpp
@@ -114,7 +114,7 @@
      * will be active at once, which is a function of the GPU's level of
      * pipelining and the frequency of queries.
      */
-    PerfMeasurementContext(size_t maxQueryCount):
+    explicit PerfMeasurementContext(size_t maxQueryCount):
             mTimingStartIndex(0),
             mTimingEndIndex(0),
             mTimingQueryIndex(0) {