Replace blink::WebDiscardableMemory with base::DiscardableMemory.

base/test/test_discardable_memory_allocator.cc

Index: base/test/test_discardable_memory_allocator.cc
diff --git a/base/test/test_discardable_memory_allocator.cc b/base/test/test_discardable_memory_allocator.cc
index eef1c982446633c79cdf94bee44ad578c55aed86..7ed0a4565ede26f6b54a011c27e0e9484c665be7 100644
--- a/base/test/test_discardable_memory_allocator.cc
+++ b/base/test/test_discardable_memory_allocator.cc
@@ -4,7 +4,8 @@
 
 #include "base/test/test_discardable_memory_allocator.h"
 
-#include <stdint.h>
+#include <cstdint>
+#include <cstring>
 
 #include "base/memory/discardable_memory.h"
 
@@ -13,12 +14,28 @@ namespace {
 
 class DiscardableMemoryImpl : public DiscardableMemory {
  public:
-  explicit DiscardableMemoryImpl(size_t size) : data_(new uint8_t[size]) {}
+  explicit DiscardableMemoryImpl(size_t size)
+      : data_(new uint8_t[size]), size_(size) {}
 
   // Overridden from DiscardableMemory:
-  bool Lock() override { return false; }
-  void Unlock() override {}
-  void* data() const override { return data_.get(); }
+  bool Lock() override {
+    DCHECK(!is_locked_);
+    is_locked_ = true;
+    return false;
+  }
+
+  void Unlock() override {
+    DCHECK(is_locked_);
+    is_locked_ = false;
+    // Force eviction to catch clients not correctly checking the return value
+    // of Lock().
+    memset(data_.get(), 0, size_);
+  }
+
+  void* data() const override {
+    DCHECK(is_locked_);
+    return data_.get();
+  }
 
   trace_event::MemoryAllocatorDump* CreateMemoryAllocatorDump(
       const char* name,
@@ -27,7 +44,9 @@ class DiscardableMemoryImpl : public DiscardableMemory {
   }
 
  private:
+  bool is_locked_ = true;
   scoped_ptr<uint8_t[]> data_;
+  size_t size_;
 };
 
 }  // namespace