Introduce ThreadedInputConnection behind a switch

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 239659a0363a470c7274804fc0f1e393085842f0..5f9eff18c5d2ffc188d17e4db5279bfc97f58964 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -16889,6 +16889,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="InputMethod.RegisterProxyView" enum="IMERegisterProxyView">
+  <owner>changwan@chromium.org</owner>
+  <summary>The result of registering proxy view to InputMethodManager.</summary>
+</histogram>
+
 <histogram name="InputMethod.VirtualKeyboard.BackspaceCount">
   <owner>shuchen@chromium.org</owner>
   <summary>
@@ -69426,6 +69431,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </int>
 </enum>
 
+<enum name="IMERegisterProxyView" type="int">
+  <int value="0" label="Success">Success in registering ProxyView to IMM</int>
+  <int value="1" label="Failure">Failure in registering ProxyView to IMM</int>
+  <int value="2" label="DetectionFailure">Failure in detecting the result</int>
+  <int value="3" label="ReplicaInputConnection">
+    ReplicaInputConnection was used instead
+  </int>
+</enum>
+
 <enum name="IMESwitchType" type="int">
   <int value="0" label="By tray menu">IME switches by tray menu</int>
   <int value="1" label="By accelerator">IME switches by accelerator</int>
@@ -71243,6 +71257,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="-1930720286" label="nacl-debug-mask"/>
   <int value="-1928198763" label="enable-async-dns"/>
   <int value="-1925117279" label="disable-quic-https"/>
+  <int value="-1919308574" label="enable-ime-thread"/>
   <int value="-1915854488" label="enable-offline-pages"/>
   <int value="-1911153473" label="enable-easy-signin"/>
   <int value="-1892555086" label="disable-compositor-animation-timelines"/>
@@ -71736,6 +71751,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="1820451991" label="enable-offline-auto-reload"/>
   <int value="1821723343" label="disable-saml-signin"/>
   <int value="1828660283" label="enable-webfonts-intervention-trigger"/>
+  <int value="1840930186" label="disable-ime-thread"/>
   <int value="1844110073" label="enable-app-view"/>
   <int value="1847024354" label="enable-hotword-hardware"/>
   <int value="1855524566" label="allow-insecure-websocket-from-https-origin"/>