[VK] Change how VirtualKeyboard.ContainerBehavior is recorded.

We move the recording of InputMethod.VirtualKeyboard.ContainerBehavior
to the end of ShowKeyboard, so we get a sample every time a floating
or docked keyboard is shown. We also account for users switching
between the two modes, as switching requires hiding and showing the
virtual keyboard.

See the bug for more about why this is needed.

Bug: 887248
Change-Id: Icd8b2fbf826a0dba7b32cabb6c7b9afcdde3fcdd
Reviewed-on: https://chromium-review.googlesource.com/1235266Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592973}

ui/keyboard/keyboard_controller.cc

@@ -717,6 +717,9 @@ void KeyboardController::PopulateKeyboardContent(
   queued_container_type_ = nullptr;
 
   ChangeState(KeyboardControllerState::SHOWN);
+
+  UMA_HISTOGRAM_ENUMERATION("InputMethod.VirtualKeyboard.ContainerBehavior",
+                            GetActiveContainerType(), ContainerType::COUNT);
 }
 
 bool KeyboardController::WillHideKeyboard() const {
@@ -853,9 +856,6 @@ void KeyboardController::SetContainerType(
     return;
   }
 
-  UMA_HISTOGRAM_ENUMERATION("InputMethod.VirtualKeyboard.ContainerBehavior",
-                            type, ContainerType::COUNT);
-
   if (state_ == KeyboardControllerState::SHOWN) {
     // Keyboard is already shown. Hiding the keyboard at first then switching
     // container type.