[geolocation] Update PositionCache histogram expiry

This updates the expiry date for two Geolocation histograms used
to evaluate the effectiveness of the network location provider
position cache:

Geolocation.PositionCache.CacheHit
Geolocation.PositionCache.CacheMiss

BUG=993080

Change-Id: I90605adef05a862e89967fa731fa39685f3fadf6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1797133
Auto-Submit: Matt Reynolds <mattreynolds@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695632}

tools/metrics/histograms/histograms.xml

@@ -48482,7 +48482,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Geolocation.PositionCache.CacheHit" units="BooleanCacheHit"
-    expires_after="2019-09-20">
+    expires_after="2020-03-10">
   <owner>mattreynolds@chromium.org</owner>
   <owner>deviceapi-team@google.com</owner>
   <summary>
@@ -48492,7 +48492,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Geolocation.PositionCache.CacheSize" units="count"
-    expires_after="2019-09-20">
+    expires_after="2020-03-10">
   <owner>mattreynolds@chromium.org</owner>
   <owner>deviceapi-team@google.com</owner>
   <summary>