base: Avoid calling VirtualAlloc with 0 length.

base/memory/discardable_shared_memory.cc

Index: base/memory/discardable_shared_memory.cc
diff --git a/base/memory/discardable_shared_memory.cc b/base/memory/discardable_shared_memory.cc
index 7449f462e68ea4936b6c381239b316da59862594..acae29eabadec0a16de0ed5e0e43f672d3faddca 100644
--- a/base/memory/discardable_shared_memory.cc
+++ b/base/memory/discardable_shared_memory.cc
@@ -221,6 +221,10 @@ DiscardableSharedMemory::LockResult DiscardableSharedMemory::Lock(
   DCHECK_EQ(locked_pages_.size(), locked_page_count_);
 #endif
 
+  // Always behave as if memory was purged when trying to lock a 0 byte segment.
+  if (!length)
+      return PURGED;
+
 // Pin pages if supported.
 #if defined(OS_ANDROID)
   SharedMemoryHandle handle = shared_memory_.handle();