Introduce RenderFrame::IsMainFrame and clean up a few things.

content/renderer/render_frame_impl_browsertest.cc

Index: content/renderer/render_frame_impl_browsertest.cc
diff --git a/content/renderer/render_frame_impl_browsertest.cc b/content/renderer/render_frame_impl_browsertest.cc
index f8f87276a71e41857619d4886a28316756b7ee51..63d51530bf0b8963ef6ad67eeb0760a4f5157cfe 100644
--- a/content/renderer/render_frame_impl_browsertest.cc
+++ b/content/renderer/render_frame_impl_browsertest.cc
@@ -33,8 +33,8 @@ class RenderFrameImplTest : public RenderViewTest {
 
   void SetUp() override {
     RenderViewTest::SetUp();
-    EXPECT_FALSE(static_cast<RenderFrameImpl*>(view_->GetMainRenderFrame())
-                     ->is_subframe_);
+    EXPECT_TRUE(static_cast<RenderFrameImpl*>(view_->GetMainRenderFrame())
+                    ->is_main_frame_);
 
     FrameMsg_NewFrame_WidgetParams widget_params;
     widget_params.routing_id = kSubframeWidgetRouteId;
@@ -54,7 +54,7 @@ class RenderFrameImplTest : public RenderViewTest {
                                  &compositor_deps_, widget_params);
 
     frame_ = RenderFrameImpl::FromRoutingID(kSubframeRouteId);
-    EXPECT_TRUE(frame_->is_subframe_);
+    EXPECT_FALSE(frame_->is_main_frame_);
   }
 
   void TearDown() override {