Adding a way to associate Android Activities with PlatformWindowAndroid

ui/aura/window_tree_host_platform.cc

Index: ui/aura/window_tree_host_platform.cc
diff --git a/ui/aura/window_tree_host_platform.cc b/ui/aura/window_tree_host_platform.cc
index 10c50132dadf2e9a3013e0b29da5dfae52d2eea8..97bc5865d403e6c734194319ad307f00c685f94f 100644
--- a/ui/aura/window_tree_host_platform.cc
+++ b/ui/aura/window_tree_host_platform.cc
@@ -11,6 +11,8 @@
 #include "ui/gfx/screen.h"
 
 #if defined(OS_ANDROID)
+#include "base/android/jni_android.h"
+#include "ui/aura/client/aura_constants.h"
 #include "ui/platform_window/android/platform_window_android.h"
 #endif
 
@@ -71,6 +73,17 @@ gfx::AcceleratedWidget WindowTreeHostPlatform::GetAcceleratedWidget() {
 }
 
 void WindowTreeHostPlatform::ShowImpl() {
+#if defined(OS_ANDROID)
+  JNIEnv* env = base::android::AttachCurrentThread();
+  jobject activity = window()->GetProperty(
+      aura::client::kActivityForRootWindow);
+  // TODO: Call into WTHPlatform.java via JNI?
+//  Java_PlatformWindowAndroid_createForActivity(

[mfomitchev, 2015/11/19 20:57:05]

We can't call into Java_PWA from here, so we'll need to create a Java class for
WTHAndroid, which would call PlatformWindowAndroid.createForActivity

[sadrul, 2015/11/20 18:32:35]

It's not clear what we would gain from calling that from here, or from
WTHAndroid::ShowImpl(), when the next line is calling into
PlatformWindowAndroid::Show(), where this call currently lives in.

[mfomitchev, 2015/11/20 18:35:01]

Well, the problem is that PWA has no reference to the Activity, and it's not
clear how it would be able to get it unless we changed PlatformWindow or
PlatformWindowDelegate interface.

This is what we talked about the other day, and you recommended we move the
logic for showing the activity to WTHAndroid instead.

[sadrul, 2015/11/20 20:04:12]

I guess it's still not clear to me how this is going to help with that. Maybe
flesh this out a bit more?

[mfomitchev, 2015/11/20 20:11:35]

Something like this:
- We will have WTHAndroid.java which will have a method
createPlatformWindowForActivity, taking the same arguments as
PlatformWindowAndroid.createForActivity.
- WTHAndroid.createPlatformWindowForActivity will just call the static method
PlatformWindowAndroid.createForActivity and return the result.
- Right in this spot where the comment is, we will call
Java_WTHAndroid_createPlatformWindowForActivity.

That's it. Basically, here we want to call into
Java_PlatformWindowAndroid_createForActivity, but JNI doesn't let us do this
directly: we need to do that through WTHAndroid.java.

Does this make sense? If not, I can code up WTHAndroid.java.

+//      env,
+//      activity,
+//      reinterpret_cast<jlong>(window_.get()),
+//      reinterpret_cast<jlong>(window_->GetPlatformImeController()));
+#endif
   window_->Show();
 }