[iOS/OSX/GN] Add -install_name to the shared_library ldflags on iOS.

build/config/mac/rules.gni

Index: build/config/mac/rules.gni
diff --git a/build/config/mac/rules.gni b/build/config/mac/rules.gni
index 2bcfbd68361c450ebb27c24881d0510df66d1cb9..8cad8424cf76be2301d5151fcdeb03652250b296 100644
--- a/build/config/mac/rules.gni
+++ b/build/config/mac/rules.gni
@@ -55,15 +55,17 @@ template("framework_bundle") {
                              "visibility",
                            ])
     output_name = _output_name
-    output_prefix_override = true
-    output_extension = ""
+    ldflags = [
+      "-install_name",
+      "@rpath/$_framework_name/$_output_name",

[Robert Sesek, 2016/04/13 15:30:58]

This isn't going to be correct in all cases, and definitely not for Content
Shell Framework and Chromium Framework. This should become a template argument
if we go this route.

However I'm hoping that if we can change the output directory for targets (per
"[gn-dev] Location of intermediate library outputs in bundles"), then we can
keep the output_extension and output_prefix_override settings, not set any
ldflags here, and then the target can have complete control over ldflags.

Also, this needs to handle the case where the shared_library target has also set
ldflags (which it will do in some cases for the component build).

[sdefresne, 2016/04/13 16:28:43]

OK. This appears to be required for iOS (at least gyp does it for EarlGrey and
OCHamcrest). I've moved it out of this template and to ios_framework_bundle when
public_headers is not empty where it should always be correct (as iOS does not
support component build).

+    ]
   }
 
   bundle_data(_shared_library_bundle_data) {
     visibility = [ ":$_framework_target" ]
     forward_variables_from(invoker, [ "testonly" ])
     sources = [
-      "$root_out_dir/${_output_name}",
+      "$root_out_dir/$shlib_prefix$_output_name$shlib_extension",
     ]
     outputs = [
       "{{bundle_executable_dir}}/$_output_name",