Bug 1223265 - Fix -Wunreachable-code and -Wimplicit-fallthrough warnings in dom/bindings and dom/ipc. r=khuey

dom/bindings/Codegen.py

@@ -4409,11 +4409,13 @@ def getJSToNativeConversionInfo(type, descriptorProvider, failureCode=None,
         templateBody = "${declName} = &${val}.toObject();\n"
 
         # For JS-implemented APIs, we refuse to allow passing objects that the
-        # API consumer does not subsume.
+        # API consumer does not subsume. The extra parens around
+        # ($${passedToJSImpl}) suppress unreachable code warnings when
+        # $${passedToJSImpl} is the literal `false`.
         if not isinstance(descriptorProvider, Descriptor) or descriptorProvider.interface.isJSImplemented():
             templateBody = fill(
                 """
-                if ($${passedToJSImpl} && !CallerSubsumes($${val})) {
+                if (($${passedToJSImpl}) && !CallerSubsumes($${val})) {
                   ThrowErrorMessage(cx, MSG_PERMISSION_DENIED_TO_PASS_ARG, "${sourceDescription}");
                   $*{exceptionCode}
                 }
@@ -5456,11 +5458,13 @@ def getJSToNativeConversionInfo(type, descriptorProvider, failureCode=None,
         templateBody = "${declName} = ${val};\n"
 
         # For JS-implemented APIs, we refuse to allow passing objects that the
-        # API consumer does not subsume.
+        # API consumer does not subsume. The extra parens around
+        # ($${passedToJSImpl}) suppress unreachable code warnings when
+        # $${passedToJSImpl} is the literal `false`.
         if not isinstance(descriptorProvider, Descriptor) or descriptorProvider.interface.isJSImplemented():
             templateBody = fill(
                 """
-                if ($${passedToJSImpl} && !CallerSubsumes($${val})) {
+                if (($${passedToJSImpl}) && !CallerSubsumes($${val})) {
                   ThrowErrorMessage(cx, MSG_PERMISSION_DENIED_TO_PASS_ARG, "${sourceDescription}");
                   $*{exceptionCode}
                 }
@@ -7319,7 +7323,7 @@ class CGCase(CGList):
         self.append(CGGeneric("case " + expression + ": {\n"))
         bodyList = CGList([body])
         if fallThrough:
-            bodyList.append(CGGeneric("/* Fall through */\n"))
+            bodyList.append(CGGeneric("MOZ_FALLTHROUGH;\n"))
         else:
             bodyList.append(CGGeneric("break;\n"))
         self.append(CGIndenter(bodyList))

dom/ipc/ContentChild.cpp

@@ -2177,8 +2177,7 @@ ContentChild::ActorDestroy(ActorDestroyReason why)
     // going through the full XPCOM shutdown path, because it doesn't
     // keep persistent state.
     QuickExit();
-#endif
-
+#else
     if (sFirstIdleTask) {
         sFirstIdleTask->Cancel();
     }
@@ -2203,6 +2202,7 @@ ContentChild::ActorDestroy(ActorDestroyReason why)
 #endif
 
     XRE_ShutdownChildProcess();
+#endif // NS_FREE_PERMANENT_DATA
 }
 
 void