text input focus: Updates WebView::GetTextInputClient when the underlying RenderView is destroyed.
This CL is split off from http://crrev.com/
785463002 .
WebView implements RenderProcessHostObserver and updates the text input client when the render process exits (i.e. the underlying RenderView / RWHVA are going to be destroyed). Because WebView::GetTextInputClient() returns RWHVA::GetTextInputClient(), we need to discard a reference to the object returned by RWHVA::GetTextInputClient() before RWHVA is destroyed.
BUG=290701
TEST=Run interactive_ui_tests.
Review URL: https://codereview.chromium.org/
862643002
Cr-Commit-Position: refs/heads/master@{#313240}