Hold a handle to the v8 context in PepperTryCatchVar.

It is safer to hold a handle to v8 context in PepperTryCatchVar than to try
retrieving it again on destruction from the frame (through the plugin instance) which has
a chance of being torn down.

BUG=411445

Review URL: https://codereview.chromium.org/562763005

Cr-Commit-Position: refs/heads/master@{#294288}

content/renderer/pepper/pepper_try_catch.cc

@@ -119,18 +119,17 @@ PepperTryCatchVar::PepperTryCatchVar(PepperPluginInstanceImpl* instance,
                                      PP_Var* exception)
     : PepperTryCatch(instance, V8VarConverter::kAllowObjectVars),
       handle_scope_(instance_->GetIsolate()),
+      context_(GetContext()),
       exception_(exception),
       exception_is_set_(false) {
-  // We switch to the plugin context.
-  v8::Handle<v8::Context> context = GetContext();
-  if (!context.IsEmpty())
-    context->Enter();
+  // We switch to the plugin context if it's not empty.
+  if (!context_.IsEmpty())
+    context_->Enter();
 }
 
 PepperTryCatchVar::~PepperTryCatchVar() {
-  v8::Handle<v8::Context> context = GetContext();
-  if (!context.IsEmpty())
-    context->Exit();
+  if (!context_.IsEmpty())
+    context_->Exit();
 }
 
 bool PepperTryCatchVar::HasException() {

content/renderer/pepper/pepper_try_catch.h

@@ -83,6 +83,8 @@ class PepperTryCatchVar : public PepperTryCatch {
   // make one for them. Note that this class is always allocated on the stack.
   v8::HandleScope handle_scope_;
 
+  v8::Handle<v8::Context> context_;
+
   v8::TryCatch try_catch_;
 
   PP_Var* exception_;