aura: Ensure OwnedMailbox not used with invalid or destroyed GLHelper.

cc/test/test_context_support.cc

Index: cc/test/test_context_support.cc
diff --git a/cc/test/test_context_support.cc b/cc/test/test_context_support.cc
index ec010fcd482f8cfe847fc7bb362aa1f6d5865d86..9558042b56081cf2442d5c8ae40861144c5735e9 100644
--- a/cc/test/test_context_support.cc
+++ b/cc/test/test_context_support.cc
@@ -19,11 +19,19 @@ TestContextSupport::~TestContextSupport() {}
 void TestContextSupport::SignalSyncPoint(uint32 sync_point,
                                          const base::Closure& callback) {
   sync_point_callbacks_.push_back(callback);
+  base::MessageLoop::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&TestContextSupport::CallAllSyncPointCallbacks,
+                 weak_ptr_factory_.GetWeakPtr()));
 }
 
 void TestContextSupport::SignalQuery(uint32 query,
                                      const base::Closure& callback) {
   sync_point_callbacks_.push_back(callback);
+  base::MessageLoop::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&TestContextSupport::CallAllSyncPointCallbacks,
+                 weak_ptr_factory_.GetWeakPtr()));
 }
 
 void TestContextSupport::SetSurfaceVisible(bool visible) {
@@ -53,7 +61,6 @@ void TestContextSupport::Swap() {
   base::MessageLoop::current()->PostTask(
       FROM_HERE, base::Bind(&TestContextSupport::OnSwapBuffersComplete,
                             weak_ptr_factory_.GetWeakPtr()));
-  CallAllSyncPointCallbacks();
 }
 
 void TestContextSupport::PartialSwapBuffers(gfx::Rect sub_buffer) {
@@ -62,7 +69,6 @@ void TestContextSupport::PartialSwapBuffers(gfx::Rect sub_buffer) {
   base::MessageLoop::current()->PostTask(
       FROM_HERE, base::Bind(&TestContextSupport::OnSwapBuffersComplete,
                             weak_ptr_factory_.GetWeakPtr()));
-  CallAllSyncPointCallbacks();
 }
 
 void TestContextSupport::SetSwapBuffersCompleteCallback(