Adds TCMalloc support for Android.

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 9fb2e162beb22621406918ec017f2dd3bc2ea073..7c84ad9f539817fbd8679de40ada7598881015c7 100644
--- a/third_party/tcmalloc/chromium/src/getpc.h
+++ b/third_party/tcmalloc/chromium/src/getpc.h
@@ -171,12 +171,19 @@ inline void* GetPC(const struct ucontext_t& signal_ucontext) {
   RAW_LOG(ERROR, "GetPC is not yet implemented on Windows\n");
   return NULL;
 }
-
+#elif defined(__ANDROID__)
+typedef int ucontext_t;
+inline void* GetPC(const ucontext_t& signal_ucontext) {
+  // Bionic doesn't export ucontext, see
+  // https://code.google.com/p/android/issues/detail?id=34784.
+  return NULL;
+}
+#else
+//
 // Normal cases.  If this doesn't compile, it's probably because
 // PC_FROM_UCONTEXT is the empty string.  You need to figure out
 // the right value for your system, and add it to the list in
 // configure.ac (or set it manually in your config.h).
-#else
 inline void* GetPC(const ucontext_t& signal_ucontext) {
   return (void*)signal_ucontext.PC_FROM_UCONTEXT;   // defined in config.h
 }