Navigation transitions: Exposed "insertCSS" to WebContents

The navigation transition needs to apply some styles during the transition, so we need to expose this call to java.

Design doc: https://docs.google.com/a/chromium.org/document/d/17jg1RRL3RI969cLwbKBIcoGDsPwqaEdBxafGNYGwiY4/edit# 
Implementation details: https://docs.google.com/a/chromium.org/document/d/1kREPtFJaeLoDKwrfmrYTD7DHCdxX1RzFBga2gNY8lyE/edit#heading=h.bng2kpmyvxq5
BUG=370696

Review URL: https://codereview.chromium.org/375073002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282504 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/web_contents/web_contents_android.cc

@@ -72,4 +72,9 @@ void WebContentsAndroid::Stop(JNIEnv* env, jobject obj) {
   web_contents_->Stop();
 }
 
+void WebContentsAndroid::InsertCSS(
+    JNIEnv* env, jobject jobj, jstring jcss) {
+  web_contents_->InsertCSS(base::android::ConvertJavaStringToUTF8(env, jcss));
+}
+
 }  // namespace content

content/browser/web_contents/web_contents_android.h

@@ -40,6 +40,8 @@ class CONTENT_EXPORT WebContentsAndroid
                                                            jobject obj) const;
   void Stop(JNIEnv* env, jobject obj);
 
+  void InsertCSS(JNIEnv* env, jobject jobj, jstring jcss);
+
  private:
   WebContents* web_contents_;
   NavigationControllerAndroid navigation_controller_;

content/public/android/java/src/org/chromium/content/browser/webcontents/WebContentsImpl.java

@@ -64,7 +64,14 @@ import org.chromium.content_public.browser.WebContents;
         nativeStop(mNativeWebContentsAndroid);
     }
 
+    @Override
+    public void insertCSS(String css) {
+        if (mNativeWebContentsAndroid == 0) return;
+        nativeInsertCSS(mNativeWebContentsAndroid, css);
+    }
+
     private native String nativeGetTitle(long nativeWebContentsAndroid);
     private native String nativeGetVisibleURL(long nativeWebContentsAndroid);
     private native void nativeStop(long nativeWebContentsAndroid);
+    private native void nativeInsertCSS(long nativeWebContentsAndroid, String css);
 }

content/public/android/java/src/org/chromium/content_public/browser/WebContents.java

@@ -27,4 +27,9 @@ public interface WebContents {
      * Stop any pending navigation.
      */
     void stop();
+
+    /**
+     * Inserts css into main frame's document.
+     */
+    void insertCSS(String css);
 }