Rename exception since original bug is fixed

This exception was created to better understand a crash stacktrace in
crbug.com/662877, and led to fixing the original cause of the crash.
However new codepaths now trigger this exception (crbug.com/822203) thus
renaming the exception message to be more generic.

Bug: 662877,822203
Change-Id: I0c1ae488b47bab739a839073f9775c7f45d0901d
Reviewed-on: https://chromium-review.googlesource.com/964387Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543431}

chrome/android/java/src/org/chromium/chrome/browser/tab/Tab.java

@@ -751,10 +751,10 @@ public class Tab
             }
 
             if (mNativeTabAndroid == 0) {
-                // if mNativeTabAndroid is invalid then we are going to crash anyways on the
+                // if mNativeTabAndroid is null then we are going to crash anyways on the
                 // native side. Lets crash on the java side so that we can have a better stack
-                // trace. https://crbug.com/662877
-                throw new RuntimeException("Please post this crash on crbug.com/662877");
+                // trace.
+                throw new RuntimeException("Tab.loadUrl called when no native side exists");
             }
 
             // We load the URL from the tab rather than directly from the ContentView so the tab has