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the original desktop IPH project which is no longer active.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.cc b/chrome/browser/flag_descriptions.cc
index 041dfc1b..b159d85 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -3255,6 +3255,11 @@
     "InstallableInkDrop is part of an InkDrop refactoring effort. This enables "
     "the pilot implementation where available.";
 
+const char kReopenTabInProductHelpName[] = "Reopen tab in-product help";
+const char kReopenTabInProductHelpDescription[] =
+    "Enable in-product help that guides a user to reopen a tab if it looks "
+    "like they accidentally closed it.";
+
 #endif  // defined(TOOLKIT_VIEWS)
 
 // Random platform combinations -----------------------------------------------
@@ -3372,15 +3377,6 @@
 
 #endif  // defined(TOOLKIT_VIEWS) || defined(OS_ANDROID)
 
-#if BUILDFLAG(ENABLE_DESKTOP_IN_PRODUCT_HELP)
-
-const char kReopenTabInProductHelpName[] = "Reopen tab in-product help";
-const char kReopenTabInProductHelpDescription[] =
-    "Enable in-product help that guides a user to reopen a tab if it looks "
-    "like they accidentally closed it.";
-
-#endif  // BUILDFLAG(ENABLE_DESKTOP_IN_PRODUCT_HELP)
-
 #if defined(WEBRTC_USE_PIPEWIRE)
 
 extern const char kWebrtcPipeWireCapturerName[] = "WebRTC PipeWire support";