Geolocation: Do nothing when its execution context is already gone.

GeoNotifier's underlying callback functions are made alive by
its execution context.  Thus, when the execution context is gone,
the underlying callback functions are also gone.

Also, it doesn't make sense anyway to invoke a callback when its
own execution context is already gone.  Thus, this patch adds
the check of the execution context before doing anything.

[email protected]

(cherry picked from commit f7c95d3)

Bug: 788975
Change-Id: I39bcbcbbe9df201924427f9d2341ba6724b5b79c
Reviewed-on: https://chromium-review.googlesource.com/798996
Commit-Queue: Yuki Shiino <[email protected]>
Reviewed-by: Kentaro Hara <[email protected]>
Reviewed-by: Hitoshi Yoshida <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#520909}
Reviewed-on: https://chromium-review.googlesource.com/816639
Reviewed-by: Yuki Shiino <[email protected]>
Cr-Commit-Position: refs/branch-heads/3282@{#94}
Cr-Branched-From: 5fdc0fa-refs/heads/master@{#520840}

Author: yuki3

third_party/WebKit/LayoutTests/geolocation-api/disconnected-frame-expected.txt

@@ -3,7 +3,7 @@ Tests that when a request is made on a Geolocation object and its Frame is disco
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
-FAIL Error callback invoked unexpectedly
+PASS No callbacks invoked
 PASS successfullyParsed is true
 
 TEST COMPLETE

third_party/WebKit/LayoutTests/geolocation-api/disconnected-frame-permission-denied-expected.txt

@@ -6,7 +6,7 @@ On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE
 PASS error.code is error.PERMISSION_DENIED
 PASS error.message is "User denied Geolocation"
 
-FAIL Error callback invoked unexpectedly
+PASS No callbacks invoked
 PASS successfullyParsed is true
 
 TEST COMPLETE

third_party/WebKit/Source/modules/geolocation/GeoNotifier.cpp

@@ -85,6 +85,12 @@ void GeoNotifier::StopTimer() {
 void GeoNotifier::TimerFired(TimerBase*) {
   timer_.Stop();
 
+  // As the timer fires asynchronously, it's possible that the execution context
+  // has already gone.  Check it first.
+  if (!geolocation_->GetExecutionContext()) {
+    return;  // Do not invoke anything because of no execution context.
+  }
+
   // Test for fatal error first. This is required for the case where the
   // LocalFrame is disconnected and requests are cancelled.
   if (fatal_error_) {