Fix to use ucontext_t in unwind.h.

third_party/tcmalloc/chromium/src/getpc.h

Index: third_party/tcmalloc/chromium/src/getpc.h
diff --git a/third_party/tcmalloc/chromium/src/getpc.h b/third_party/tcmalloc/chromium/src/getpc.h
index c5183bf0adba86f8d5ecb13a30e81de032905839..0d622b3b1af123d2b7e1fd151e80a29800c3bfdd 100644
--- a/third_party/tcmalloc/chromium/src/getpc.h
+++ b/third_party/tcmalloc/chromium/src/getpc.h
@@ -175,13 +175,15 @@ inline void* GetPC(const struct ucontext_t& signal_ucontext) {
   return NULL;
 }
 #elif defined(__ANDROID__)
+namespace tcmalloc {
 typedef struct _Unwind_Context ucontext_t;
+}
 
-inline void* GetPC(const ucontext_t& signal_ucontext) {
+inline void* GetPC(const tcmalloc::ucontext_t& signal_ucontext) {
   // Bionic doesn't export ucontext, see
   // https://code.google.com/p/android/issues/detail?id=34784.
   return reinterpret_cast<void*>(_Unwind_GetIP(
-      const_cast<ucontext_t*>(&signal_ucontext)));
+      const_cast<tcmalloc::ucontext_t*>(&signal_ucontext)));
 }
 //
 // Normal cases.  If this doesn't compile, it's probably because