LayoutLib: Correctly resolve ?attr/foo [DO NOT MERGE]

?attr/foo in platform files wasn't resolved properly. The IDE checked
the app namespace for the attribute even though it is being referenced
from a platform file.

Change-Id: I7db6dfef5b540d99804c298120578da9d060b886
(cherry picked from commit e21c7ec8a02922a6bec19436897f9ee02be3d6c2)

tools/layoutlib/bridge/src/com/android/layoutlib/bridge/android/BridgeContext.java

@@ -560,7 +560,7 @@ public final class BridgeContext extends Context {
         StyleResourceValue customStyleValues = null;
         if (customStyle != null) {
             ResourceValue item = mRenderResources.findResValue(customStyle,
-                    false /*forceFrameworkOnly*/);
+                    isPlatformFile /*forceFrameworkOnly*/);
 
             // resolve it in case it links to something else
             item = mRenderResources.resolveResValue(item);