Fix google-explicit-constructor warnings in system/tpm.

* Declare explicit conversion constructors.

Bug: 28341362
Change-Id: If68be8b0d92fdaea99e54388fbe0104213926480
Test: build with clang-tidy
diff --git a/tpm_manager/server/binder_service.h b/tpm_manager/server/binder_service.h
index c4de0c6..bda64ef 100644
--- a/tpm_manager/server/binder_service.h
+++ b/tpm_manager/server/binder_service.h
@@ -55,7 +55,7 @@
   friend class NvramServiceInternal;
   class NvramServiceInternal : public android::tpm_manager::BnTpmNvram {
    public:
-    NvramServiceInternal(TpmNvramInterface* service);
+    explicit NvramServiceInternal(TpmNvramInterface* service);
     ~NvramServiceInternal() override = default;
 
     // ITpmNvram interface.
@@ -95,7 +95,7 @@
   friend class OwnershipServiceInternal;
   class OwnershipServiceInternal : public android::tpm_manager::BnTpmOwnership {
    public:
-    OwnershipServiceInternal(TpmOwnershipInterface* service);
+    explicit OwnershipServiceInternal(TpmOwnershipInterface* service);
     ~OwnershipServiceInternal() override = default;
 
     // ITpmOwnership interface.
diff --git a/trunks/trunks_binder_service.h b/trunks/trunks_binder_service.h
index d9c8dec..d26730f 100644
--- a/trunks/trunks_binder_service.h
+++ b/trunks/trunks_binder_service.h
@@ -52,7 +52,7 @@
   friend class BinderServiceInternal;
   class BinderServiceInternal : public android::trunks::BnTrunks {
    public:
-    BinderServiceInternal(TrunksBinderService* service);
+    explicit BinderServiceInternal(TrunksBinderService* service);
     ~BinderServiceInternal() override = default;
 
     // ITrunks interface.
diff --git a/trunks/trunks_client_test.cc b/trunks/trunks_client_test.cc
index eb60b19..74b4305 100644
--- a/trunks/trunks_client_test.cc
+++ b/trunks/trunks_client_test.cc
@@ -841,7 +841,7 @@
   };
   class Scoper {
    public:
-    Scoper(const base::Closure& callback) : callback_(callback) {}
+    explicit Scoper(const base::Closure& callback) : callback_(callback) {}
     ~Scoper() {
       if (!cancel_)
         callback_.Run();