Move desktop in-product help code out of build flag

Desktop in-product help code was built only when a flag,
ENABLE_DESKTOP_IN_PRODUCT_HELP, was enabled. This was a holdover from
the original desktop IPH project which is no longer active. It is more
appopriate to gate this behind a base::Feature flag instead.

This CL makes all curerntly active IPH code build on all desktop
platforms without using a build flag.

The original build flag is renamed to
ENABLE_LEGACY_DESKTOP_IN_PRODUCT_HELP, set to false by default, and
the old IPH project is kept behind this. This was done since this code
violates layering: it resides in chrome/browser, but directly accesses
code in chrome/browser/ui/ and chrome/browser/ui/views.

Bug: 938720
Change-Id: I3850f61a8802c320d9cc0aa8d49721ccdb711d93
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1643891
Reviewed-by: Scott Violet <[email protected]>
Reviewed-by: Tommy Nyquist <[email protected]>
Reviewed-by: Peter Kasting <[email protected]>
Commit-Queue: Collin Baker <[email protected]>
Cr-Commit-Position: refs/heads/master@{#666748}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 76aef53..7264790 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -10,7 +10,6 @@
 #include "build/build_config.h"
 #include "build/buildflag.h"
 #include "chrome/common/buildflags.h"
-#include "components/feature_engagement/buildflags.h"
 #include "components/nacl/common/buildflags.h"
 #include "device/vr/buildflags/buildflags.h"
 #include "media/media_buildflags.h"
@@ -1958,6 +1957,9 @@
 extern const char kInstallableInkDropName[];
 extern const char kInstallableInkDropDescription[];
 
+extern const char kReopenTabInProductHelpName[];
+extern const char kReopenTabInProductHelpDescription[];
+
 #endif  // defined(TOOLKIT_VIEWS)
 
 // Random platform combinations -----------------------------------------------
@@ -2053,12 +2055,6 @@
 
 #endif  // defined(TOOLKIT_VIEWS) || defined(OS_ANDROID)
 
-#if BUILDFLAG(ENABLE_DESKTOP_IN_PRODUCT_HELP)
-
-extern const char kReopenTabInProductHelpName[];
-extern const char kReopenTabInProductHelpDescription[];
-
-#endif  // BUILDFLAG(ENABLE_DESKTOP_IN_PRODUCT_HELP)
 extern const char kAvoidFlashBetweenNavigationName[];
 extern const char kAvoidFlahsBetweenNavigationDescription[];