Code:   void OnDidAddMessageToConsole(int32_t,
                                const base::string16& message,
                                int32_t,
                                const base::string16&) {
    callback_.Run(message);
  }

Vulnerability Type: 
CWE ID: CWE-416
Summary: A use after free in Google Chrome prior to 56.0.2924.76 for Linux, Windows and Mac, and 56.0.2924.87 for Android, allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.
Commit Message: Convert FrameHostMsg_DidAddMessageToConsole to Mojo.

Note: Since this required changing the test
RenderViewImplTest.DispatchBeforeUnloadCanDetachFrame, I manually
re-introduced https://crbug.com/666714 locally (the bug the test was
added for), and reran the test to confirm that it still covers the bug.

Bug: 786836
Change-Id: I110668fa6f0f261fd2ac36bb91a8d8b31c99f4f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1526270
Commit-Queue: Lowell Manners <lowell@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653137}