Fix google-explicit-constructor warnings in vulkan.

* Add explicit keyword to conversion constructors.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: I13c32bd5bc53fe897df58eda331ff70ebcf0b349
diff --git a/vulkan/libvulkan/debug_report.h b/vulkan/libvulkan/debug_report.h
index be9b645..3d8bd50 100644
--- a/vulkan/libvulkan/debug_report.h
+++ b/vulkan/libvulkan/debug_report.h
@@ -85,9 +85,9 @@
 
 class DebugReportLogger {
    public:
-    DebugReportLogger(const VkInstanceCreateInfo& info)
+    explicit DebugReportLogger(const VkInstanceCreateInfo& info)
         : instance_pnext_(info.pNext), callbacks_(nullptr) {}
-    DebugReportLogger(const DebugReportCallbackList& callbacks)
+    explicit DebugReportLogger(const DebugReportCallbackList& callbacks)
         : instance_pnext_(nullptr), callbacks_(&callbacks) {}
 
     void Message(VkDebugReportFlagsEXT flags,