Adding a way to associate Android Activities with PlatformWindowAndroid

ui/platform_window/android/platform_window_android.cc

Index: ui/platform_window/android/platform_window_android.cc
diff --git a/ui/platform_window/android/platform_window_android.cc b/ui/platform_window/android/platform_window_android.cc
index 0cfdc6bf8504e06f67ff6fd03f1ec7e036572ff3..63eaabbff80224e6aede9ecf3b0dafc79dc1bc7c 100644
--- a/ui/platform_window/android/platform_window_android.cc
+++ b/ui/platform_window/android/platform_window_android.cc
@@ -52,6 +52,12 @@ bool PlatformWindowAndroid::Register(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
+//static
+PlatformWindowAndroid* PlatformWindowAndroid::From(
+    PlatformWindow* platform_window) {
+  return static_cast<PlatformWindowAndroid*>(platform_window);
+}
+
 PlatformWindowAndroid::PlatformWindowAndroid(PlatformWindowDelegate* delegate)
     : delegate_(delegate),
       window_(NULL),
@@ -70,6 +76,25 @@ PlatformWindowAndroid::~PlatformWindowAndroid() {
   }
 }
 
+void PlatformWindowAndroid::AttachToActivity(
+    JNIEnv* env,
+    const base::android::JavaRef<jobject>& activity) {
+  DCHECK(!IsAttachedToActivity());
+  DCHECK(!activity.is_null());
+  base::android::ScopedJavaLocalRef<jobject> jpwa =
+      Java_PlatformWindowAndroid_createForActivity(
+          env,
+          activity.obj(),
+          reinterpret_cast<jlong>(this),
+          reinterpret_cast<jlong>(&platform_ime_controller_));
+  java_platform_window_android_ = JavaObjectWeakGlobalRef(env, jpwa.obj());
+}
+
+bool PlatformWindowAndroid::IsAttachedToActivity() const {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  return !java_platform_window_android_.get(env).is_null();
+}
+
 void PlatformWindowAndroid::Destroy(JNIEnv* env, jobject obj) {
   delegate_->OnClosed();
 }
@@ -154,14 +179,7 @@ void PlatformWindowAndroid::ReleaseWindow() {
 // PlatformWindowAndroid, PlatformWindow implementation:
 
 void PlatformWindowAndroid::Show() {
-  if (!java_platform_window_android_.is_empty())
-    return;
-  JNIEnv* env = base::android::AttachCurrentThread();
-  java_platform_window_android_ = JavaObjectWeakGlobalRef(
-      env, Java_PlatformWindowAndroid_createForActivity(
-               env, base::android::GetApplicationContext(),
-               reinterpret_cast<jlong>(this),
-               reinterpret_cast<jlong>(&platform_ime_controller_)).obj());
+  DCHECK(IsAttachedToActivity());
 }
 
 void PlatformWindowAndroid::Hide() {