blink_gc_plugin: retire overloaded traceImpl detection and handling.

tools/clang/blink_gc_plugin/tests/traceimpl_error.txt

Index: tools/clang/blink_gc_plugin/tests/traceimpl_error.txt
diff --git a/tools/clang/blink_gc_plugin/tests/traceimpl_error.txt b/tools/clang/blink_gc_plugin/tests/traceimpl_error.txt
index ec976a084d1ca2b05b25aa5bf4d2d794f9136e08..86bef28b66f9e45dffa7baa6e19669f90c0a083e 100644
--- a/tools/clang/blink_gc_plugin/tests/traceimpl_error.txt
+++ b/tools/clang/blink_gc_plugin/tests/traceimpl_error.txt
@@ -1,20 +1,20 @@
 In file included from traceimpl_error.cpp:5:
-./traceimpl_error.h:23:3: warning: [blink-gc] Class 'TraceImplInlinedWithUntracedMember' has untraced fields that require tracing.
-  void TraceImpl(VisitorDispatcher visitor) {
+./traceimpl_error.h:20:3: warning: [blink-gc] Class 'TraceImplInlinedWithUntracedMember' has untraced fields that require tracing.
+  void Trace(Visitor* visitor) {
   ^
-./traceimpl_error.h:28:3: note: [blink-gc] Untraced field 'x_' declared here:
+./traceimpl_error.h:25:3: note: [blink-gc] Untraced field 'x_' declared here:
   Member<X> x_;
   ^
-./traceimpl_error.h:53:3: warning: [blink-gc] Base class 'Base' of derived class 'TraceImplInlineWithUntracedBase' requires tracing.
-  void TraceImpl(VisitorDispatcher visitor) {
+./traceimpl_error.h:44:3: warning: [blink-gc] Base class 'Base' of derived class 'TraceImplInlineWithUntracedBase' requires tracing.
+  void Trace(Visitor* visitor) override {
   ^
-traceimpl_error.cpp:14:1: warning: [blink-gc] Class 'TraceImplExternWithUntracedMember' has untraced fields that require tracing.
-inline void TraceImplExternWithUntracedMember::TraceImpl(
+traceimpl_error.cpp:9:1: warning: [blink-gc] Class 'TraceImplExternWithUntracedMember' has untraced fields that require tracing.
+void TraceImplExternWithUntracedMember::Trace(Visitor* visitor) {
 ^
-./traceimpl_error.h:40:3: note: [blink-gc] Untraced field 'x_' declared here:
+./traceimpl_error.h:34:3: note: [blink-gc] Untraced field 'x_' declared here:
   Member<X> x_;
   ^
-traceimpl_error.cpp:24:1: warning: [blink-gc] Base class 'Base' of derived class 'TraceImplExternWithUntracedBase' requires tracing.
-inline void TraceImplExternWithUntracedBase::TraceImpl(
+traceimpl_error.cpp:13:1: warning: [blink-gc] Base class 'Base' of derived class 'TraceImplExternWithUntracedBase' requires tracing.
+void TraceImplExternWithUntracedBase::Trace(Visitor* visitor) {
 ^
 4 warnings generated.