Add UMA to study the effect of defaulting fullscreen video to landscape mode

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 0f4947ceaa71e02fd198af349a25fd95e865745f..fddc9925821811fe4bf34038eb81ca20dcc4874d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -12225,6 +12225,76 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="MobileFullscreenVideo.DurationAfterPotraitRotation"
+    units="milliseconds">
+  <owner>qinmin@chromium.org</owner>
+  <summary>
+    Android: Records the duration that a fullscreen video is played after device
+    rotates from portrait to landscape mode for the first time, and before it
+    exits fullscreen. If there is no device rotation or if the video starts with
+    landscape mode, it is not recorded. If there are mutiple rotations between
+    portrait and landscape mode, only one record is emitted and it is equal to
+    the time period from the first rotation to the moment when the video exits
+    fullscreen.
+  </summary>
+</histogram>
+
+<histogram name="MobileFullscreenVideo.LandscapeDuration" units="milliseconds">
+  <owner>qinmin@chromium.org</owner>
+  <summary>
+    Android: Records the duration that a fullscreen video is played in landscape
+    mode. If a video starts playing in landscape mode, and then it is switched
+    back and forth between landscape and portrait mode, only the time period
+    before the first switch is accounted. If a video starts playing in portrait
+    mode, it is not recorded.
+  </summary>
+</histogram>
+
+<histogram name="MobileFullscreenVideo.LandscapeRotation" enum="BooleanEnabled">
+  <owner>qinmin@chromium.org</owner>
+  <summary>
+    Android: Records whether a fullscreen video is switched from landscape to
+    portrait mode at any point during playback.
+  </summary>
+</histogram>
+
+<histogram name="MobileFullscreenVideo.OrientationPortrait"
+    enum="BooleanEnabled">
+  <owner>qinmin@chromium.org</owner>
+  <summary>
+    Android: Records the device orientation when a video enters fullscreen. The
+    value is true if device orientation is portrait, or false otherwise. The
+    video doesn't necessarily needs to be in a playing state.
+  </summary>
+</histogram>
+
+<histogram name="MobileFullscreenVideo.PortraitDuration" units="milliseconds">
+  <owner>qinmin@chromium.org</owner>
+  <summary>
+    Android: Records the duration that a fullscreen video is played in portrait
+    mode. If a video starts playing in portrait mode, and then it is switched
+    back and forth between landscape and portrait mode, only the time period
+    before the first switch is accounted. If a video starts playing in landscape
+    mode, it is not recorded.
+  </summary>
+</histogram>
+
+<histogram name="MobileFullscreenVideo.PortraitRotation" enum="BooleanEnabled">
+  <owner>qinmin@chromium.org</owner>
+  <summary>
+    Android: Records whether a fullscreen video is switched from portrait to
+    landscape mode at any point during playback.
+  </summary>
+</histogram>
+
+<histogram name="MobileFullscreenVideo.VideoPortrait" enum="BooleanEnabled">
+  <owner>qinmin@chromium.org</owner>
+  <summary>
+    Android: Records whether a video has a larger height than width when it
+    enters the fullscreen mode.
+  </summary>
+</histogram>
+
 <histogram name="MobileStartup.MobileMultiWindowInstances">
   <owner>dtrainor@chromium.org</owner>
   <summary>