Create base::win::MemoryPressureMonitor class.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 982467c5bbefc189ab2d657bdd8a435dec405cb8..b7a18b3c5031b5260f447cadbf6c5526b646a6b4 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -15221,6 +15221,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Memory.PressureLevel" enum="MemoryPressureLevel">
+  <owner>chrisha@chromium.org</owner>
+  <summary>
+    The memory pressure level, which is recorded periodically (once per second).
+    This is used to show the relative time that systems spend in each of the
+    memory pressure states.
+  </summary>
+</histogram>
+
 <histogram name="Memory.ProcessCount">
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
@@ -56605,6 +56614,12 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="1" label="Http Live Stream Type"/>
 </enum>
 
+<enum name="MemoryPressureLevel" type="int">
+  <int value="0" label="No memory pressure"/>
+  <int value="1" label="Moderate memory pressure"/>
+  <int value="2" label="Critical memory pressure"/>
+</enum>
+
 <enum name="MetadataReadResult" type="int">
   <int value="0" label="Success"/>
   <int value="1" label="Open failure"/>