Support changing style parent in overlays

Package overlays makes it possible for vendors to tweak the look of
the platform and the applications without touching any platform or
application code directly. This makes package overlays an important
mechanism in the Android build system.

There is currently a limitation that forbids changing the parent of a
style. If vendors could change the parent of e.g. ‘CalendarTheme’
from Android’s vanilla ‘Theme’ to ‘VendorTheme’, then vendor
specific adjustments could be done without changing any code directly.

From looking at the code it can be seen that the parent value of a
style is stored temporarily in ResourceTable::Entry::mParent while
overlays are gone through in buildResources(), and processed (in
ResourceTable::Entry::assignResourceIds()) at first after all overlays
have been handled, so there aren’t any obvious reasons why changing
parent in an overlay should be forbidden.

Change-Id: I5969bb8aab90df437e1967fc504cc0da79107d13

Author: Martin Nordholts

tools/aapt/ResourceTable.cpp

@@ -1629,13 +1629,6 @@ status_t ResourceTable::startBag(const SourcePos& sourcePos,
 
     // If a parent is explicitly specified, set it.
     if (bagParent.size() > 0) {
-        String16 curPar = e->getParent();
-        if (curPar.size() > 0 && curPar != bagParent) {
-            sourcePos.error("Conflicting parents specified, was '%s', now '%s'\n",
-                            String8(e->getParent()).string(),
-                            String8(bagParent).string());
-            return UNKNOWN_ERROR;
-        }
         e->setParent(bagParent);
     }
 
@@ -1683,13 +1676,6 @@ status_t ResourceTable::addBag(const SourcePos& sourcePos,
 
     // If a parent is explicitly specified, set it.
     if (bagParent.size() > 0) {
-        String16 curPar = e->getParent();
-        if (curPar.size() > 0 && curPar != bagParent) {
-            sourcePos.error("Conflicting parents specified, was '%s', now '%s'\n",
-                    String8(e->getParent()).string(),
-                    String8(bagParent).string());
-            return UNKNOWN_ERROR;
-        }
         e->setParent(bagParent);
     }