Let ImeAdapterAndroid have the same lifecycle as its Java peer

The native ImeAdapterAndroid(IAA) instance is owned by
RenderWidgetHostViewAndroid(RWHVA) while its Java peer
(ImeAdapter) is owned by CVC. This causes their life
cycles to be different. Attach/detach API are used to get them
linked before talking to each other.

This CL makes this mechanism simpler by having Java ImeAdapter
class create the native together, hence gets their lifetime synced.
The separate attach/detach mechanism is not necessary since
the native is an WebContentObserver, and connected to (or
disconnected from) RWHVA accordingly when notified of RenderView-
Host update callback. Connecting to interstitial page is also
taken care of by observing the appropriate callbacks.

BUG=662908

Review-Url: https://codereview.chromium.org/2752113005
Cr-Original-Original-Commit-Position: refs/heads/master@{#460028}
Committed: https://chromium.googlesource.com/chromium/src/+/153d2811b3cbcf69cda7ab4817cdc35e7c680dee
Review-Url: https://codereview.chromium.org/2752113005
Cr-Original-Commit-Position: refs/heads/master@{#461024}
Committed: https://chromium.googlesource.com/chromium/src/+/d01dcc6a7955b96aff2083461319208afc2bc9ca
Review-Url: https://codereview.chromium.org/2752113005
Cr-Commit-Position: refs/heads/master@{#461975}
diff --git a/content/browser/BUILD.gn b/content/browser/BUILD.gn
index ae7db20..e72d55a 100644
--- a/content/browser/BUILD.gn
+++ b/content/browser/BUILD.gn
@@ -1793,6 +1793,8 @@
       "android/date_time_chooser_android.cc",
       "android/date_time_chooser_android.h",
       "android/gesture_event_type.h",
+      "android/ime_adapter_android.cc",
+      "android/ime_adapter_android.h",
       "android/interstitial_page_delegate_android.cc",
       "android/interstitial_page_delegate_android.h",
       "android/java/gin_java_bound_object.cc",
@@ -1833,8 +1835,6 @@
       "media/capture/screen_capture_device_android.h",
       "renderer_host/compositor_impl_android.cc",
       "renderer_host/compositor_impl_android.h",
-      "renderer_host/ime_adapter_android.cc",
-      "renderer_host/ime_adapter_android.h",
       "renderer_host/input/synthetic_gesture_target_android.cc",
       "renderer_host/input/synthetic_gesture_target_android.h",
       "renderer_host/native_web_keyboard_event_android.cc",