Updated MallocHooks to collect stack traces when memory is allocated.

runtime/vm/os_android.cc

Index: runtime/vm/os_android.cc
diff --git a/runtime/vm/os_android.cc b/runtime/vm/os_android.cc
index 1ce9650dea08310d64c14465f8666e979017991d..f3673ee49992916d52721afcef5d2d99a8d50759 100644
--- a/runtime/vm/os_android.cc
+++ b/runtime/vm/os_android.cc
@@ -276,6 +276,12 @@ void OS::DebugBreak() {
 }
 
 
+uintptr_t DART_NOINLINE OS::GetProgramCounter() {
+  return reinterpret_cast<uintptr_t>(
+      __builtin_extract_return_addr(__builtin_return_address(0)));
+}
+
+
 char* OS::StrNDup(const char* s, intptr_t n) {
   return strndup(s, n);
 }