Revert of Android: Trust large random numbers for temp files

build/android/devil/android/device_temp_file.py

Index: build/android/devil/android/device_temp_file.py
diff --git a/build/android/devil/android/device_temp_file.py b/build/android/devil/android/device_temp_file.py
index 01a91d4524c7390cf9312847dc3eb08b9b3a05de..cd9e8db5613f11f1b2f229853cafa4110359494d 100644
--- a/build/android/devil/android/device_temp_file.py
+++ b/build/android/devil/android/device_temp_file.py
@@ -6,17 +6,25 @@
 
 # pylint: disable=W0622
 
-import posixpath
-import random
 import threading
 
 from devil.android import device_errors
 from devil.utils import cmd_helper
 
+_COMMAND_TEMPLATE = (
+    # Make sure that the temp dir is writable
+    'test -d {dir} && '
+    # If 5 random attempts fail, something is up.
+    'for i in 1 2 3 4 5; do '
+    'fn={dir}/{prefix}-$(date +%s)-"$RANDOM"{suffix};'
+    'test -e "$fn" || break;'
+    'done && '
+    # Touch the file, so other temp files can't get the same name.
+    'touch "$fn" && echo -n "$fn"')
 
 class DeviceTempFile(object):
   def __init__(self, adb, suffix='', prefix='temp_file', dir='/data/local/tmp'):
-    """Find an unused temporary file path on the device.
+    """Find an unused temporary file path in the devices external directory.
 
     When this object is closed, the file will be deleted on the device.
 
@@ -27,9 +35,11 @@
       dir: The directory on the device where to place the temp file.
     """
     self._adb = adb
-    # Python's random module use 52-bit numbers according to its docs.
-    random_hex = hex(random.randint(0, 2 ** 52))[2:]
-    self.name = posixpath.join(dir, '%s-%s%s' % (prefix, random_hex, suffix))
+    command = _COMMAND_TEMPLATE.format(
+        dir=cmd_helper.SingleQuote(dir),
+        suffix=cmd_helper.SingleQuote(suffix),
+        prefix=cmd_helper.SingleQuote(prefix))
+    self.name = self._adb.Shell(command)
     self.name_quoted = cmd_helper.SingleQuote(self.name)
 
   def close(self):