Revert of components: Make user_prefs a source_set. (patchset #1 id:1 of https://codereview.chromium.org/1258653002/)

Reason for revert:
Try to fix UserPrefs::Get() crashes.

Original issue's description:
> components: Make user_prefs a source_set.
>
> This is a tiny component, it does not need to be a shared libray in the
> component build.
>
> BUG=None
> [email protected]
>
> Committed: https://crrev.com/f8a72db8313967a512ea94c05b3951c255a4b796
> Cr-Commit-Position: refs/heads/master@{#340349}

[email protected],[email protected]
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=None

Review URL: https://codereview.chromium.org/1254123002

Cr-Commit-Position: refs/heads/master@{#340401}
diff --git a/components/user_prefs.gypi b/components/user_prefs.gypi
index 53b08b4..3554d0d 100644
--- a/components/user_prefs.gypi
+++ b/components/user_prefs.gypi
@@ -6,7 +6,7 @@
   'targets': [
     {
       'target_name': 'user_prefs',
-      'type': 'static_library',
+      'type': '<(component)',
       'dependencies': [
         '../base/base.gyp:base',
         '../base/base.gyp:base_prefs',
@@ -14,9 +14,13 @@
       'include_dirs': [
         '..',
       ],
+      'defines': [
+        'USER_PREFS_IMPLEMENTATION',
+      ],
       'sources': [
         'user_prefs/user_prefs.cc',
         'user_prefs/user_prefs.h',
+        'user_prefs/user_prefs_export.h',
       ],
     },
   ],