Revert "base: Implement browser process support for discardable memory."

base/memory/discardable_memory_shmem_allocator.cc

Index: base/memory/discardable_memory_shmem_allocator.cc
diff --git a/base/memory/discardable_memory_shmem_allocator.cc b/base/memory/discardable_memory_shmem_allocator.cc
index a87c58d415d480d2cac8b7dc30389222d78e557f..761204f31220d043e526f6cb35e3548e6eca237f 100644
--- a/base/memory/discardable_memory_shmem_allocator.cc
+++ b/base/memory/discardable_memory_shmem_allocator.cc
@@ -11,6 +11,45 @@
 namespace base {
 namespace {
 
+class DiscardableMemoryShmemChunkImpl : public DiscardableMemoryShmemChunk {
+ public:
+  explicit DiscardableMemoryShmemChunkImpl(
+      scoped_ptr<DiscardableSharedMemory> shared_memory)
+      : shared_memory_(shared_memory.Pass()) {}
+
+  // Overridden from DiscardableMemoryShmemChunk:
+  bool Lock() override { return false; }
+  void Unlock() override {
+    shared_memory_->Unlock(0, 0);
+    shared_memory_.reset();
+  }
+  void* Memory() const override { return shared_memory_->memory(); }
+
+ private:
+  scoped_ptr<DiscardableSharedMemory> shared_memory_;
+
+  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryShmemChunkImpl);
+};
+
+// Default allocator implementation that allocates in-process
+// DiscardableSharedMemory instances.
+class DiscardableMemoryShmemAllocatorImpl
+    : public DiscardableMemoryShmemAllocator {
+ public:
+  // Overridden from DiscardableMemoryShmemAllocator:
+  scoped_ptr<DiscardableMemoryShmemChunk>
+  AllocateLockedDiscardableMemory(size_t size) override {
+    scoped_ptr<DiscardableSharedMemory> memory(new DiscardableSharedMemory);
+    if (!memory->CreateAndMap(size))
+      return nullptr;
+
+    return make_scoped_ptr(new DiscardableMemoryShmemChunkImpl(memory.Pass()));
+  }
+};
+
+LazyInstance<DiscardableMemoryShmemAllocatorImpl>::Leaky g_default_allocator =
+    LAZY_INSTANCE_INITIALIZER;
+
 DiscardableMemoryShmemAllocator* g_allocator = nullptr;
 
 }  // namespace
@@ -30,7 +69,9 @@ void DiscardableMemoryShmemAllocator::SetInstance(
 // static
 DiscardableMemoryShmemAllocator*
 DiscardableMemoryShmemAllocator::GetInstance() {
-  DCHECK(g_allocator);
+  if (!g_allocator)
+    g_allocator = g_default_allocator.Pointer();
+
   return g_allocator;
 }