Add "q=preview" directive on main frame requests on poor networks

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 96aa9d340dd8ff37185f7f12be4b03ba44ba1304..2fcbf9b8526d7a3092b35ffb782a031335b62419 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1783,6 +1783,12 @@ const FeatureEntry kFeatureEntries[] = {
      IDS_FLAGS_DATA_REDUCTION_PROXY_LO_FI_DESCRIPTION,
      kOsAll,
      MULTI_VALUE_TYPE(kDataReductionProxyLoFiChoices)},
+    {"enable-data-reduction-proxy-lo-fi-preview",
+     IDS_FLAGS_ENABLE_DATA_REDUCTION_PROXY_LO_FI_PREVIEW_NAME,
+     IDS_FLAGS_ENABLE_DATA_REDUCTION_PROXY_LO_FI_PREVIEW_DESCRIPTION,
+     kOsAll,
+     SINGLE_VALUE_TYPE(
+         data_reduction_proxy::switches::kEnableDataReductionProxyLoFiPreview)},

[Alexei Svitkine (slow), 2015/11/24 18:57:06]

Given this is a new flag, I suggest using the base/feature_list.h API for this
instead.

See announcement here:

https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/Esavy4-JTHY

[megjablon, 2015/11/24 19:38:11]

For organization purposes, I'd like to the keep the switch the way it is now.
This is layered on top of the lo-fi switch, and it is confusing to enable the
two switches in different ways. Also, this feature does not need a disable
switch.

     {"clear-data-reduction-proxy-data-savings",
      IDS_FLAGS_DATA_REDUCTION_PROXY_RESET_SAVINGS_NAME,
      IDS_FLAGS_DATA_REDUCTION_PROXY_RESET_SAVINGS_DESCRIPTION,