lacros: Add Profile::IsDefaultProfile

This CL adds a stub for Profile::IsDefaultProfile. This is required for
Lacros since exactly 1 browser profile will be associated with the
chromeOS device's signed in profile.

Bug: 1129543
Change-Id: I74566593fc60d887a20c7f10974687619588e3cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2416816Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Reviewed-by: Kush Sinha <sinhak@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Auto-Submit: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809362}

chrome/browser/profiles/profile.h

@@ -16,6 +16,7 @@
 #include "base/observer_list.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
+#include "build/chromeos_buildflags.h"
 #include "content/public/browser/browser_context.h"
 #include "mojo/public/cpp/bindings/remote.h"
 #include "services/network/public/mojom/network_context.mojom-forward.h"
@@ -417,6 +418,13 @@ class Profile : public content::BrowserContext {
   // Returns whether it is a system profile.
   virtual bool IsSystemProfile() const;
 
+#if BUILDFLAG(IS_LACROS)
+  // TODO(https://crbug.com/1129543): Implement this method.
+  // In Lacros, there is exactly one profile associated with the currently
+  // logged in user on ChromeOS.
+  bool IsDefaultProfile() const { return false; }
+#endif
+
   bool CanUseDiskWhenOffTheRecord() override;
 
   // Did the user restore the last session? This is set by SessionRestore.