For #10434: Handle cases when proc/$pid/stat is not accessible.

app/metrics.yaml

@@ -2253,6 +2253,22 @@ startup.timeline:
       - perf-android-fe@mozilla.com
       - mcomella@mozilla.com
     expires: "2020-07-15"
+  framework_start_read_error:
+    send_in_pings:
+      - startup-timeline
+    type: boolean
+    description: |
+      An error when attempting to read stats from /proc pseudo-filesystem -
+      privacy managers can block access to reading these files -
+      the application will catch a file reading exception.
+    bugs:
+      - https://github.com/mozilla-mobile/fenix/issues/10434
+    data_reviews:
+      - https://github.com/mozilla-mobile/fenix/pull/10481
+    notification_emails:
+      - perf-android-fe@mozilla.com
+      - mcomella@mozilla.com
+    expires: "2020-07-15"
   clock_ticks_per_second:
     send_in_pings:
       - startup-timeline

app/src/main/java/org/mozilla/fenix/perf/StartupFrameworkStartMeasurement.kt

@@ -6,6 +6,7 @@ package org.mozilla.fenix.perf
 
 import android.os.Process
 import android.os.SystemClock
+import java.io.FileNotFoundException
 import kotlin.math.roundToLong
 import org.mozilla.fenix.GleanMetrics.StartupTimeline as Telemetry
 
@@ -53,14 +54,23 @@ internal class StartupFrameworkStartMeasurement(
         if (applicationInitNanos < 0) {
             telemetry.frameworkStartError.set(true)
         } else {
-            telemetry.frameworkStart.setRawNanos(getFrameworkStartNanos())
+            try {
+                telemetry.frameworkStart.setRawNanos(getFrameworkStartNanos())
+            } catch (e: FileNotFoundException) {
+                // Privacy managers can add hooks that block access to reading system /proc files.
+                // We want to catch these exception and report an error on accessing the file
+                // rather than an implementation error.
+                telemetry.frameworkStartReadError.set(true)
+            }
 
             // frameworkStart is derived from the number of clock ticks per second. To ensure this
             // value does not throw off our result, we capture it too.
             telemetry.clockTicksPerSecond.add(stat.clockTicksPerSecond.toInt())
         }
     }
-
+    /**
+     * @throws [java.io.FileNotFoundException]
+     */
     private fun getFrameworkStartNanos(): Long {
         // Get our timestamps in ticks: we expect ticks to be less granular than nanoseconds so,
         // to ensure our measurement uses the correct number of significant figures, we convert

app/src/main/java/org/mozilla/fenix/perf/Stat.kt

@@ -24,6 +24,9 @@ private const val FIELD_POS_STARTTIME = 21 // starttime naming matches field in
  */
 open class Stat {
 
+    /**
+     * @throws [java.io.FileNotFoundException]
+     */
     @VisibleForTesting(otherwise = PRIVATE)
     open fun getStatText(pid: Int): String = File("/proc/$pid/stat").readText()