Splits components/sessions into separate core and content targets.

components/sessions.gypi

Index: components/sessions.gypi
diff --git a/components/sessions.gypi b/components/sessions.gypi
index f05d028e6e1b1241474699486d87b5a79acac9eb..efcf197cdbb84982b05a73a3aa914f1af38c47dd 100644
--- a/components/sessions.gypi
+++ b/components/sessions.gypi
@@ -3,10 +3,28 @@
 # found in the LICENSE file.
 
 {
+  'variables': {
+    # Core sources shared by sessions_content and sessions_ios.
+    #
+    # TODO(rohitrao): We are including these sources directly into each

[blundell, 2014/10/24 14:10:42]

I think this still doesn't explain the key issue, which is that sessions_core
can't be a <(component) due to the fact that it declares a static function that
it doesn't define.

I really don't think that the decision of whether to split up sessions_core into
its own target is dependent on how large the set of core sources is, fwiw. 

+    # individual target in order to avoid the complications associated with
+    # making a separate sessions_core target.  Because sessions_content is a
+    # shared_library, depending directly on static libraries can cause issues.
+    # Since sessions is still a small target, it is simplest to just share these
+    # sources across targets.  Revisit if sessions grows large enough that it
+    # makes sense to split out a separate sessions_core target.
+    'sessions_core_sources': [
+      'sessions/core/serialized_navigation_driver.h',
+      'sessions/serialized_navigation_entry.cc',
+      'sessions/serialized_navigation_entry.h',
+      'sessions/session_id.cc',
+      'sessions/session_id.h',
+    ],
+  },
   'targets': [
     {
-      # GN version: //components/sessions
-      'target_name': 'sessions',
+      # GN version: //components/sessions:sessions_content
+      'target_name': 'sessions_content',
       'type': '<(component)',
       'dependencies': [
         '../base/base.gyp:base',
@@ -25,18 +43,12 @@
       ],
       'sources': [
         # Note: sources list duplicated in GN build.
+        '<@(sessions_core_sources)',
 
-        # TODO(rohitrao): Split this target into three separate core, content,
-        # and web targets.
         'sessions/content/content_serialized_navigation_builder.cc',
         'sessions/content/content_serialized_navigation_builder.h',
         'sessions/content/content_serialized_navigation_driver.cc',
         'sessions/content/content_serialized_navigation_driver.h',
-        'sessions/core/serialized_navigation_driver.h',
-        'sessions/serialized_navigation_entry.cc',
-        'sessions/serialized_navigation_entry.h',
-        'sessions/session_id.cc',
-        'sessions/session_id.h',
       ],
       'conditions': [
         ['android_webview_build == 0', {