mac: Weakly link against the CoreBluetooth framework.

device/BUILD.gn

Index: device/BUILD.gn
diff --git a/device/BUILD.gn b/device/BUILD.gn
index 3bf6fa77878d31482b8f299773bb4a027d5cba20..becef455c1dcb84cec65d1ae4ec61103470c1b65 100644
--- a/device/BUILD.gn
+++ b/device/BUILD.gn
@@ -112,5 +112,13 @@ test("device_unittests") {
 
   if (is_mac) {
     libs = [ "IOBluetooth.framework" ]
+
+    # In the OSX 10.10 SDK, CoreBluetooth became a top level framework.
+    # Previously, it was nested in IOBluetooth. In order for Chrome to run on
+    # OSes older than OSX 10.10, the top level CoreBluetooth framework must be
+    # weakly linked.
+    if (mac_sdk_version == "10.10") {
+      ldflags = [ "-weak_framework CoreBluetooth" ]
+    }
   }
 }