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..4c056c0fc80b89f50ba982f97e2b4cee89aa7dd3 100644
--- a/content/browser/android/content_view_core_impl.cc
+++ b/content/browser/android/content_view_core_impl.cc
@@ -215,7 +215,7 @@ ContentViewCoreImpl::ContentViewCoreImpl(
       view_(view_android_delegate),
       web_contents_(static_cast<WebContentsImpl*>(web_contents)),
       page_scale_(1),
-      dpi_scale_(ui::GetScaleFactorForNativeView(&view_)),
+      dpi_scale_(1),

[boliu, 2016/10/18 00:26:25]

why is this change needed?

[Tima Vaisburd, 2016/10/19 01:15:54]

It is actually not needed, but I wanted to make it consistent with the Java side
and make it clear that DIP scale will be explicitly set.
I reverted this change.
I also changed the initial DIP scale in RenderCoordinates.java from 0 to 1.

       device_orientation_(0),
       accessibility_enabled_(false) {
   CHECK(web_contents) <<
@@ -803,6 +803,15 @@ float ContentViewCoreImpl::GetBottomControlsHeightDip() const {
   return GetBottomControlsHeightPix() / dpi_scale();
 }
 
+void ContentViewCoreImpl::ForceLayout() {

[boliu, 2016/10/18 00:26:25]

just call this "WasResized"?

[Tima Vaisburd, 2016/10/19 01:15:54]

WasResized() already existed, now it sets the physical size and then calls this
ForceLayout(). See below.

+  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();
+}
+
 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(