Check for constructor first when installing tracing stubs.

Addresses comments in
https://android-review.googlesource.com/#/c/104383/ made after the commit.

Bug: 16386215

(cherry picked from commit 5afe466c027c6ac821bf7c9a88cd7de5260a639b)

Change-Id: Ic81161d0b96a0633c4c534a93172cff59312fa61
diff --git a/runtime/instrumentation.cc b/runtime/instrumentation.cc
index d5c6e4f..47d35f3 100644
--- a/runtime/instrumentation.cc
+++ b/runtime/instrumentation.cc
@@ -121,11 +121,9 @@
     // Do not change stubs for these methods.
     return;
   }
-  std::string temp;
-  // Note that the Proxy class itself is not a proxy class.
-  if (strcmp(method->GetDeclaringClass()->GetDescriptor(&temp), "Ljava/lang/reflect/Proxy;") == 0 &&
-      method->IsConstructor()) {
-    // Do not stub Proxy.<init>.
+  // Don't stub Proxy.<init>. Note that the Proxy class itself is not a proxy class.
+  if (method->IsConstructor() &&
+      method->GetDeclaringClass()->DescriptorEquals("Ljava/lang/reflect/Proxy;")) {
     return;
   }
   const void* new_portable_code;