Add basic Chrome interaction with the mash shelf.

chrome/common/pref_names.h

Index: chrome/common/pref_names.h
diff --git a/chrome/common/pref_names.h b/chrome/common/pref_names.h
index 813916e434ed834f7bc987a9d17d619f9e21474d..4ed0022100fee2ea056d57ac04a8fd8ee9f76c34 100644
--- a/chrome/common/pref_names.h
+++ b/chrome/common/pref_names.h
@@ -703,7 +703,7 @@ extern const char kMediaGalleriesUniqueId[];
 extern const char kMediaGalleriesRememberedGalleries[];
 #endif  // !defined(OS_ANDROID)
 
-#if defined(USE_ASH)
+#if defined(USE_AURA)

[James Cook, 2016/04/06 04:29:52]

Possibly silly drive-by question: Why does all this need to move into USE_AURA
instead of living in USE_ASH? I see the source files moving between groups in
gyp/gn, but I don't understand why. Why does chrome_mash_shelf_controller.cc
compile using USE_AURA but not USE_ASH? I must have missed something. Maybe I've
forgotten how USE_AURA and USE_ASH interact.

[msw, 2016/04/07 20:34:57]

afaik, we want to be able to build mash w/o USE_ASH for ease of development.
I think we to remove USE_ASH and just rely on OS_CHROMEOS and runtime flags.

 extern const char kShelfAlignment[];
 extern const char kShelfAlignmentLocal[];
 extern const char kShelfAutoHideBehavior[];
@@ -715,9 +715,7 @@ extern const char kLogoutDialogDurationMs[];
 extern const char kPinnedLauncherApps[];
 extern const char kPolicyPinnedLauncherApps[];
 extern const char kShowLogoutButtonInTray[];
-#endif
 
-#if defined(USE_AURA)
 extern const char kMaxSeparationForGestureTouchesInPixels[];
 extern const char kSemiLongPressTimeInMs[];
 extern const char kTabScrubActivationDelayInMs[];