Added MemoryMonitor for Linux (with test)

components/memory_coordinator/browser/memory_monitor_linux.cc

Index: components/memory_coordinator/browser/memory_monitor_linux.cc
diff --git a/components/memory_coordinator/browser/memory_monitor_linux.cc b/components/memory_coordinator/browser/memory_monitor_linux.cc
new file mode 100644
index 0000000000000000000000000000000000000000..bd1cf500dae38fe9b9b3c490cdaef5bdff130379
--- /dev/null
+++ b/components/memory_coordinator/browser/memory_monitor_linux.cc
@@ -0,0 +1,54 @@
+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/memory_coordinator/browser/memory_monitor_linux.h"
+
+#include "base/memory/ptr_util.h"
+#include "base/process/process_metrics.h"
+
+namespace memory_coordinator {
+
+namespace {
+
+// A global static instance of the default delegate. Used by default by
+// MemoryMonitorLinux.
+MemoryMonitorDelegate g_memory_monitor_delegate;
+
+// The number of bits to shift to convert KiB to MiB.
+const int kShiftKiBtoMiB = 10;
+
+}  // namespace
+
+MemoryMonitorLinux::MemoryMonitorLinux(MemoryMonitorDelegate* delegate)
+    : delegate_(delegate) {}
+
+int MemoryMonitorLinux::GetFreeMemoryUntilCriticalMB() {
+  base::SystemMemoryInfoKB mem_info = {};
+  delegate_->GetSystemMemoryInfo(&mem_info);
+
+  // According to kernel commit 34e431b0ae398fc54ea69ff85ec700722c9da773,
+  // "available" is the "amount of memory that is available for a new workload
+  // without pushing the system into swap"; return that value if it is valid.
+  // Old linux kernels (before 3.14) don't support "available" and show zero
+  // instead.
+  if (mem_info.available > 0)
+    return mem_info.available >> kShiftKiBtoMiB;
+
+  // If there is no "available" value, guess at it based on free memory and
+  // what the OS can easily discard.
+  return (mem_info.free + mem_info.buffers + mem_info.cached) >> kShiftKiBtoMiB;
+}
+
+// static
+std::unique_ptr<MemoryMonitorLinux> MemoryMonitorLinux::Create(
+    MemoryMonitorDelegate* delegate) {
+  return base::MakeUnique<MemoryMonitorLinux>(delegate);
+}
+
+// Implementation of factory function defined in memory_monitor.h.
+std::unique_ptr<MemoryMonitor> CreateMemoryMonitor() {
+  return MemoryMonitorLinux::Create(&g_memory_monitor_delegate);
+}
+
+}  // namespace memory_coordinator