Add UMA metric to track the time elapsed since a WebAPK was last launched

chrome/android/java/src/org/chromium/chrome/browser/metrics/WebApkUma.java

Index: chrome/android/java/src/org/chromium/chrome/browser/metrics/WebApkUma.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/metrics/WebApkUma.java b/chrome/android/java/src/org/chromium/chrome/browser/metrics/WebApkUma.java
index 75850a2dea08197f32fb3ff39028d4650d668da5..4a3a0423b0a2394e2684a2e24aa4afd66c88c72d 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/metrics/WebApkUma.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/metrics/WebApkUma.java
@@ -132,4 +132,13 @@ public class WebApkUma {
                 : "WebApk.ShellApkVersion.UnboundApk";
         RecordHistogram.recordSparseSlowlyHistogram(name, shellApkVersion);
     }
+
+    /**
+     * Recorded when a WebAPK is launched from the homescreen. Records the time elapsed since the
+     * previous WebAPK launch. Not recorded the first time that a WebAPK is launched.
+     */
+    public static void recordLaunchInterval(long intervalMs) {
+        RecordHistogram.recordCustomTimesHistogram("WebApk.LaunchInterval", intervalMs,
+                TimeUnit.HOURS.toMillis(1), TimeUnit.DAYS.toMillis(30), TimeUnit.MILLISECONDS, 50);
+    }
 }