Fix an IME regression for <webview> due to missing IPC message param

The IPC message BrowserPluginHostMsg_ImeFinishComposingText does not have a
parameter for the instance ID of BrowserPlugin and therefore, is dropped on
the browser side inside BrowserPluginMessageFilter. This causes a regression
in (Japanese) IME where clicking during an ongoing composition does not commit.

BUG=720023

Review-Url: https://codereview.chromium.org/2887973002
Cr-Commit-Position: refs/heads/master@{#473976}

content/browser/browser_plugin/browser_plugin_guest.cc

@@ -920,7 +920,10 @@ void BrowserPluginGuest::OnImeCommitText(
                                   replacement_range, relative_cursor_pos));
 }
 
-void BrowserPluginGuest::OnImeFinishComposingText(bool keep_selection) {
+void BrowserPluginGuest::OnImeFinishComposingText(
+    int browser_plugin_instance_id,
+    bool keep_selection) {
+  DCHECK_EQ(browser_plugin_instance_id_, browser_plugin_instance_id);
   Send(new InputMsg_ImeFinishComposingText(routing_id(), keep_selection));
 }
 

content/browser/browser_plugin/browser_plugin_guest.h

@@ -343,7 +343,7 @@ class CONTENT_EXPORT BrowserPluginGuest : public GuestHost,
       const std::vector<blink::WebCompositionUnderline>& underlines,
       const gfx::Range& replacement_range,
       int relative_cursor_pos);
-  void OnImeFinishComposingText(bool keep_selection);
+  void OnImeFinishComposingText(int instance_id, bool keep_selection);
   void OnExtendSelectionAndDelete(int instance_id, int before, int after);
   void OnImeCancelComposition();
 #if defined(OS_MACOSX) || defined(USE_AURA)

content/common/browser_plugin/browser_plugin_messages.h

@@ -58,7 +58,10 @@ IPC_STRUCT_END()
 // These messages are from the embedder to the browser process.
 // Most messages from the embedder to the browser process are CONTROL because
 // they are routed to the appropriate BrowserPluginGuest based on the
-// browser_plugin_instance_id which is unique per embedder process.
+// |browser_plugin_instance_id| which is unique per embedder process.
+// |browser_plugin_instance_id| is only used by BrowserPluginMessageFilter to
+// find the right BrowserPluginGuest. It should not be needed by the final IPC
+// handler.
 
 // This message is sent from BrowserPlugin to BrowserPluginGuest to issue an
 // edit command.
@@ -89,7 +92,8 @@ IPC_MESSAGE_CONTROL5(
 
 // This message is sent from BrowserPlugin to BrowserPluginGuest to notify that
 // inserting the current composition is requested.
-IPC_MESSAGE_CONTROL1(BrowserPluginHostMsg_ImeFinishComposingText,
+IPC_MESSAGE_CONTROL2(BrowserPluginHostMsg_ImeFinishComposingText,
+                     int /* browser_plugin_instance_id */,
                      bool /* keep selection */)
 
 // Deletes the current selection plus the specified number of characters before

content/renderer/browser_plugin/browser_plugin.cc

@@ -604,7 +604,8 @@ bool BrowserPlugin::FinishComposingText(
   bool keep_selection =
       (selection_behavior == blink::WebInputMethodController::kKeepSelection);
   BrowserPluginManager::Get()->Send(
-      new BrowserPluginHostMsg_ImeFinishComposingText(keep_selection));
+      new BrowserPluginHostMsg_ImeFinishComposingText(
+          browser_plugin_instance_id_, keep_selection));
   // TODO(kochi): This assumes the IPC handling always succeeds.
   return true;
 }