Refactor direct_memory_pressure_calculator.h per platform.

components/memory_pressure/direct_memory_pressure_calculator_win.cc

Index: components/memory_pressure/direct_memory_pressure_calculator_win.cc
diff --git a/components/memory_pressure/direct_memory_pressure_calculator_win.cc b/components/memory_pressure/direct_memory_pressure_calculator_win.cc
index 25d7d7bf50e9d52f44e958649e5ce56364ab0302..5381cbf7466f19075e893a934a6411df3b428a54 100644
--- a/components/memory_pressure/direct_memory_pressure_calculator_win.cc
+++ b/components/memory_pressure/direct_memory_pressure_calculator_win.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "components/memory_pressure/direct_memory_pressure_calculator.h"
+#include "components/memory_pressure/direct_memory_pressure_calculator_win.h"
 
 namespace memory_pressure {
 
@@ -82,6 +82,11 @@ DirectMemoryPressureCalculator::CalculateCurrentPressureLevel() {
   return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
 }
 
+bool DirectMemoryPressureCalculator::GetSystemMemoryInfo(
+    base::SystemMemoryInfoKB* mem_info) const {
+  return base::GetSystemMemoryInfo(mem_info);
+}
+
 void DirectMemoryPressureCalculator::InferThresholds() {
   // Determine if the memory installed is 'large' or 'small'. Default to 'large'
   // on failure, which uses more conservative thresholds.