Use a valid /prefetch argument when launching a process.

content/public/common/DEPS

Index: content/public/common/DEPS
diff --git a/content/public/common/DEPS b/content/public/common/DEPS
index 55a793f00067ea0fed224e73ed081757f1381d29..544a8c369b109cadc1897b8452aa38943f15a054 100644
--- a/content/public/common/DEPS
+++ b/content/public/common/DEPS
@@ -4,5 +4,10 @@ specific_include_rules = {
   ],
   "media_stream_request.h": [
     "+media/audio/audio_parameters.h",
-  ]
+  ],
+  "prefetch_argument_win.cc": [
+    # TODO(fdoray): Remove this once the PreRead field trial expires.
+    #               crbug.com/577698
+    "+components/startup_metric_utils/common/pre_read_field_trial_utils_win.h"

[jam, 2016/01/20 23:17:36]

content shouldn't depend on this component, even temporarily.

[fdoray, 2016/01/21 01:39:51]

Could I add the /prefetch argument in
ChromeContentBrowserClient::AppendExtraCommandLineSwitches to avoid changing
content/? I tried to do this in another CL [1], but I was told that:
- This shouldn't be in done chrome/, as all users of content/ should be able to
benefit from this optimization.
- It is better to set a prefetch id at the time a command line is created than
to inspect an existing command line to determine which prefetch id to use [2].

Note: content already depends on this component startup_metric_utils_common.
This component allows us to read the PreRead field trial options from the
registry. The options are stored in the registry because they are needed before
variations are read from the disk [4]. If we read the options from the registry
in some cases and from variations::GetVariationParamValue in other cases, we
could end up using different sets of options in the same process...

[1]
https://codereview.chromium.org/1595633002/diff/60001/chrome/browser/chrome_c...
[2]
https://codereview.chromium.org/1595633002/diff/20001/chrome/common/prefetch_...
[3]
https://code.google.com/p/chromium/codesearch#chromium/src/content/content_re...
[4]
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/app/main_dl...

+  ],
 }