Adds a reference to web contents/container view in Tab class

This is a preparatory CL for upcoming changes that will remove API
getWebContents/getContainerView from ContentViewCore. Tab defines
direct references to WebContents and container view. WebContents is
passed to |initialize| and ContentView is created as the container
view in |createContentViewCore|, so it doesn't need to access them
indirectly through CVC. They are set in |setContentViewCore| and
nulled out in |destroyContentViewCore| to keep their validity in sync.

Accompanying changes for cleanup:

- Deleted |getActiveContentViewCore|. Other method of similar name
  |getContentViewCore| returns null if Tab is showing native view or
  rendered content is already destroyed. So using it instead is
  enough for all the callsites that already have null checks or tests
  that know all the preconditions.

- |getContentView| always returns container view for non-native page.
  In fact it is what it was already doing - just made it clearer by
  removing some dead code in it. Its return type is ViewGroup, and
  will be used as a replacement for CVC.getContainerView() in other classes.

Bug: 598880
Change-Id: I0c5966b69f6871ce53aa5ffadb73a76214ad35b2
Reviewed-on: https://chromium-review.googlesource.com/1018561Reviewed-by: Yash Malik <ymalik@chromium.org>
Reviewed-by: Maria Khomenko <mariakhomenko@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552206}

chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java

@@ -854,7 +854,7 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
         for (TabModel model : getTabModelSelector().getModels()) {
             int count = model.getCount();
             for (int i = 0; i < count; ++i) {
-                ContentViewCore cvc = model.getTabAt(i).getActiveContentViewCore();
+                ContentViewCore cvc = model.getTabAt(i).getContentViewCore();
                 if (cvc != null) cvc.onResume();
             }
         }
@@ -892,7 +892,7 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
         for (TabModel model : getTabModelSelector().getModels()) {
             int count = model.getCount();
             for (int i = 0; i < count; ++i) {
-                ContentViewCore cvc = model.getTabAt(i).getActiveContentViewCore();
+                ContentViewCore cvc = model.getTabAt(i).getContentViewCore();
                 if (cvc != null) cvc.onPause();
             }
         }

chrome/android/java/src/org/chromium/chrome/browser/compositor/CompositorViewHolder.java

@@ -420,7 +420,7 @@ public class CompositorViewHolder extends FrameLayout
 
     private ContentViewCore getActiveContent() {
         Tab tab = getCurrentTab();
-        return tab != null ? tab.getActiveContentViewCore() : null;
+        return tab != null ? tab.getContentViewCore() : null;
     }
 
     private WebContents getActiveWebContents() {
@@ -922,8 +922,7 @@ public class CompositorViewHolder extends FrameLayout
             onPhysicalBackingSizeChanged(
                     webContents, mCompositorView.getWidth(), mCompositorView.getHeight());
         }
-        View view = tab.getContentView();
-        if (view == null || (tab.isNativePage() && view == tab.getView())) return;
+        if (tab.isNativePage() || tab.getView() == null) return;
         tab.setTopControlsHeight(getTopControlsHeightPixels(), controlsResizeView());
         tab.setBottomControlsHeight(getBottomControlsHeightPixels());
     }

chrome/android/javatests/src/org/chromium/chrome/browser/vr_shell/VrShellControllerInputTest.java

@@ -88,8 +88,7 @@ public class VrShellControllerInputTest {
                 VrTestFramework.getHtmlTestFile("test_controller_scrolling"), PAGE_LOAD_TIMEOUT_S);
         final WebContents wc = mVrTestRule.getActivity().getActivityTab().getWebContents();
         Coordinates coord = Coordinates.createFor(wc);
-        waitForPageToBeScrollable(
-                mVrTestRule.getActivity().getActivityTab().getActiveContentViewCore());
+        waitForPageToBeScrollable(mVrTestRule.getActivity().getActivityTab().getContentViewCore());
 
         // Test that scrolling down works
         int startScrollPoint = coord.getScrollYPixInt();
@@ -139,8 +138,7 @@ public class VrShellControllerInputTest {
                 VrTestFramework.getHtmlTestFile("test_controller_scrolling"), PAGE_LOAD_TIMEOUT_S);
         final WebContents wc = mVrTestRule.getActivity().getActivityTab().getWebContents();
         Coordinates coord = Coordinates.createFor(wc);
-        waitForPageToBeScrollable(
-                mVrTestRule.getActivity().getActivityTab().getActiveContentViewCore());
+        waitForPageToBeScrollable(mVrTestRule.getActivity().getActivityTab().getContentViewCore());
 
         // Arbitrary, but valid values to trigger fling scrolling
         int scrollSteps = 2;