Add observers for DIP scale change.

content/browser/android/content_view_core_impl.cc

Index: content/browser/android/content_view_core_impl.cc
diff --git a/content/browser/android/content_view_core_impl.cc b/content/browser/android/content_view_core_impl.cc
index 7854c3e44ecb2dd4432142a395239ddef0b483d0..fe0af7a6a09b3a584e93a25f8bb83f0530c3efe2 100644
--- a/content/browser/android/content_view_core_impl.cc
+++ b/content/browser/android/content_view_core_impl.cc
@@ -803,6 +803,15 @@ float ContentViewCoreImpl::GetBottomControlsHeightDip() const {
   return GetBottomControlsHeightPix() / dpi_scale();
 }
 
+void ContentViewCoreImpl::ForceLayout() {

[boliu, 2016/10/19 04:19:18]

naming is hard, but definitely avoid overloading terms like "Layout". How about
SendScreenRects then?

[Tima Vaisburd, 2016/10/19 20:25:11]

The modestly looking |view->WasResized();| eventually calls
RenderWidgetHostImpl::WasResized()
https://cs.chromium.org/chromium/src/content/browser/renderer_host/render_wid...
which obtains resize parameters, checks whether they are changed and sends
ViewMsg_Resize
to the renderer process. I renamed this method into
SendScreenRectsAndresizeWidget() for now,
maybe you can come up with a better name.
My intention was to initiate the layout process though.

+  RenderWidgetHostViewAndroid* view = GetRenderWidgetHostViewAndroid();
+  if (view) {
+    // |SendScreenRects()| indirectly calls GetViewSize() that asks Java layer.
+    web_contents_->SendScreenRects();
+    view->WasResized();
+  }
+}
+
 void ContentViewCoreImpl::MoveRangeSelectionExtent(const gfx::PointF& extent) {
   if (!web_contents_)
     return;
@@ -868,6 +877,15 @@ void ContentViewCoreImpl::SetFocus(JNIEnv* env,
   SetFocusInternal(focused);
 }
 
+void ContentViewCoreImpl::SetDIPScale(JNIEnv* env,
+                                      const JavaParamRef<jobject>& obj,
+                                      jfloat dipScale,
+                                      jboolean forceLayout) {
+  dpi_scale_ = dipScale;
+  if (forceLayout)
+    ForceLayout();

[boliu, 2016/10/19 04:19:18]

only if changed?

[Tima Vaisburd, 2016/10/19 20:25:11]

Yes, I added that.
Now I realized that during reparenting we might send resize twice...

+}
+
 void ContentViewCoreImpl::SetFocusInternal(bool focused) {
   if (!GetRenderWidgetHostViewAndroid())
     return;
@@ -1236,16 +1254,12 @@ void ContentViewCoreImpl::RemoveJavascriptInterface(
 
 void ContentViewCoreImpl::WasResized(JNIEnv* env,
                                      const JavaParamRef<jobject>& obj) {
-  RenderWidgetHostViewAndroid* view = GetRenderWidgetHostViewAndroid();
   gfx::Size physical_size(
       Java_ContentViewCore_getPhysicalBackingWidthPix(env, obj),
       Java_ContentViewCore_getPhysicalBackingHeightPix(env, obj));
   view_.GetLayer()->SetBounds(physical_size);
 
-  if (view) {
-    web_contents_->SendScreenRects();
-    view->WasResized();
-  }
+  ForceLayout();
 }
 
 long ContentViewCoreImpl::GetNativeImeAdapter(