Oilpan: Prepare moving DateTimeChooser to Oilpan

Source/platform/DateTimeChooserClient.h

Index: Source/platform/DateTimeChooserClient.h
diff --git a/Source/platform/DateTimeChooserClient.h b/Source/platform/DateTimeChooserClient.h
index 0cc3d190e35d7a92c68ba2282f0d02ffcde8bf07..e4f6123614ea9a709044e1ebf38f672f2f62c116 100644
--- a/Source/platform/DateTimeChooserClient.h
+++ b/Source/platform/DateTimeChooserClient.h
@@ -32,20 +32,22 @@
 #define DateTimeChooserClient_h
 
 #include "platform/PlatformExport.h"
+#include "platform/heap/Handle.h"
 #include "wtf/text/WTFString.h"
 
 namespace WebCore {
 
-class PLATFORM_EXPORT DateTimeChooserClient {
+class PLATFORM_EXPORT DateTimeChooserClient : public WillBeGarbageCollectedMixin {

[sof, 2014/06/14 06:18:01]

This subtly breaks the non-Oilpan component build, as it will instantiate
WebCore::DummyBase<void> in blink_platform _and_ implicitly export the derived
template instantiation (at least MSVC does, see
http://msdn.microsoft.com/en-us/library/twa2aw10.aspx 's last bullet point.) The
linker will then complain when it links blink_web, as it also has that
instantiation.

The best solution I could come up with was to let that DummyBase instantiation
be exported from blink_platform & have everyone else import it, see
https://codereview.chromium.org/302093011/patch/80001/90008. There are some
relevant comments on that review as well, I think. That CL is not going ahead,
so feel free to re-purpose :)

+    DECLARE_EMPTY_VIRTUAL_DESTRUCTOR_WILL_BE_REMOVED(DateTimeChooserClient);
 public:
-    virtual ~DateTimeChooserClient();
-
     // Called when user picked a value.
     virtual void didChooseValue(const String&) = 0;
     // Called when user picked a value.
     virtual void didChooseValue(double) = 0;
     // Called when chooser has ended.
     virtual void didEndChooser() = 0;
+
+    virtual void trace(Visitor*) { }
 };
 
 } // namespace WebCore