Unbreak release component builds after #777386.

Going for the smallest fix to heal the bots; lizeb can fix better
(if necessary) tomorrow.

TBR=lizeb@chromium.org

Bug: 1094908
Change-Id: I45f4afd916f02a87015aa967e7c5ea449fe0df8e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2246933Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#778605}

base/allocator/partition_allocator/partition_alloc.cc

@@ -467,6 +467,17 @@ void* PartitionReallocGenericFlags(PartitionRoot<thread_safe>* root,
 #endif
 }  // namespace base
 
+template void* PartitionReallocGenericFlags<false>(PartitionRoot<false>*,
+                                                   int,
+                                                   void*,
+                                                   size_t,
+                                                   const char*);
+template void* PartitionReallocGenericFlags<true>(PartitionRoot<true>*,
+                                                  int,
+                                                  void*,
+                                                  size_t,
+                                                  const char*);
+
 template <bool thread_safe>
 void* PartitionRoot<thread_safe>::Realloc(void* ptr,
                                           size_t new_size,

base/allocator/partition_allocator/partition_alloc.h

@@ -343,6 +343,7 @@ ALWAYS_INLINE void* PartitionRoot<thread_safe>::Alloc(size_t size,
   return AllocFlags(0, size, type_name);
 }
 
+// Explicitly instantantiated in the .cc file.
 template <bool thread_safe>
 BASE_EXPORT void* PartitionReallocGenericFlags(PartitionRoot<thread_safe>* root,
                                                int flags,