Move stress_cache to the tools directory

BUG=none
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/963163004

Cr-Commit-Position: refs/heads/master@{#319109}

net/BUILD.gn

@@ -956,7 +956,7 @@ if (!is_ios && !is_android) {
   executable("stress_cache") {
     testonly = true
     sources = [
-      "disk_cache/blockfile/stress_cache.cc",
+      "tools/stress_cache/stress_cache.cc",
     ]
 
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.

net/net.gyp

@@ -1470,7 +1470,7 @@
             'net_test_support',
           ],
           'sources': [
-            'disk_cache/blockfile/stress_cache.cc',
+            'tools/stress_cache/stress_cache.cc',
           ],
           # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
           'msvs_disabled_warnings': [4267, ],