Added the ability to inspect an element's style

This pull request adds the ability to view the style of an element that is selected in the elements tree using the same UI as what is shown in the styles tab when inspecting an element of a webpage.

Some gotchas:

* The names of style properties shown are not copied verbatim from the names of fields in the `View` class, but are translated to a format that Chrome understands. For example, `View` has a field called `paddingLeft`, but in order for that to be rendered correctly in Chrome, it needs to be transmitted as `padding-left`.

* Default values are not transmitted, unless they are of an enum type, in which case they are *always* transmitted.

* Due to inconsistencies between annotations present on certain Android SDK versions, some fields that are enums are not translated into their string representation. This is unfortunate, but the only way to get around it is by special-casing those one or two cases, which is probably not viable long-term.

Some things that would be nice to add in the future:

* Inferring some way the element's style 'class', so that the styles aren't all aggregated into one blob. Same with style inheritance.

* In Chrome you can edit these CSS properties, but here you can't. Maybe a future project? Would probably relatively simple to add.

Style inspection of Stetho's 'Settings' button:

<p align="center">
<img src="https://cloud.githubusercontent.com/assets/2636237/9415188/5872116c-47f2-11e5-8764-ebb2bd43bcbf.png">

<img src="https://cloud.githubusercontent.com/assets/2636237/9415244/ad7b3350-47f2-11e5-97de-7d84772b3021.png">
</p>

Author: ichub

stetho/src/main/java/com/facebook/stetho/Stetho.java

@@ -259,14 +259,14 @@ public DefaultInspectorModulesBuilder remove(String moduleName) {
 
     public Iterable<ChromeDevtoolsDomain> finish() {
       provideIfDesired(new Console());
-      provideIfDesired(new CSS());
       provideIfDesired(new Debugger());
       if (Build.VERSION.SDK_INT >= AndroidDOMConstants.MIN_API_LEVEL) {
         Document document = new Document(
             new AndroidDocumentProviderFactory(
                 (Application) mContext.getApplicationContext()));
 
         provideIfDesired(new DOM(document));
+        provideIfDesired(new CSS(document));
       }
       provideIfDesired(new DOMStorage(mContext));
       provideIfDesired(new HeapProfiler());

stetho/src/main/java/com/facebook/stetho/common/ListUtil.java

@@ -65,6 +65,10 @@ public static <T> List<T> copyToImmutableList(List<T> list) {
     }
   }
 
+  public static <T> List<T> newImmutableList(T item) {
+    return new OneItemImmutableList<>(item);
+  }
+
   private static interface ImmutableList<E> extends List<E>, RandomAccess {
   }
 

stetho/src/main/java/com/facebook/stetho/inspector/elements/AbstractChainedDescriptor.java

@@ -144,4 +144,14 @@ public final void setAttributesAsText(Object element, String text) {
   protected void onSetAttributesAsText(E element, String text) {
     mSuper.setAttributesAsText(element, text);
   }
+
+  @Override
+  @SuppressWarnings("unchecked")
+  public final void getStyles(Object element, StyleAccumulator accumulator) {
+    mSuper.getStyles(element, accumulator);
+    onGetStyles((E) element, accumulator);
+  }
+
+  protected void onGetStyles(E element, StyleAccumulator accumulator) {
+  }
 }

stetho/src/main/java/com/facebook/stetho/inspector/elements/Document.java

@@ -140,6 +140,12 @@ public void setAttributesAsText(Object element, String text) {
     mDocumentProvider.setAttributesAsText(element, text);
   }
 
+  public void getElementStyles(Object element, StyleAccumulator styleAccumulator) {
+    NodeDescriptor nodeDescriptor = getNodeDescriptor(element);
+
+    nodeDescriptor.getStyles(element, styleAccumulator);
+  }
+
   public DocumentView getDocumentView() {
     verifyThreadAccess();
     return mShadowDocument;

stetho/src/main/java/com/facebook/stetho/inspector/elements/NodeDescriptor.java

@@ -33,4 +33,6 @@ public interface NodeDescriptor extends ThreadBound {
   void getAttributes(Object element, AttributeAccumulator attributes);
 
   void setAttributesAsText(Object element, String text);
+
+  void getStyles(Object element, StyleAccumulator accumulator);
 }

stetho/src/main/java/com/facebook/stetho/inspector/elements/ObjectDescriptor.java

@@ -51,4 +51,8 @@ public void getAttributes(Object element, AttributeAccumulator attributes) {
   @Override
   public void setAttributesAsText(Object element, String text) {
   }
+
+  @Override
+  public void getStyles(Object element, StyleAccumulator accumulator) {
+  }
 }

stetho/src/main/java/com/facebook/stetho/inspector/elements/Origin.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.stetho.inspector.elements;
+
+import com.facebook.stetho.json.annotation.JsonValue;
+
+public enum Origin {
+  INJECTED("injected"),
+  USER_AGENT("user-agent"),
+  INSPECTOR("inspector"),
+  REGULAR("regular");
+
+  private final String mValue;
+
+  Origin(String value) {
+    mValue = value;
+  }
+
+  @JsonValue
+  public String getProtocolValue() {
+    return mValue;
+  }
+}

stetho/src/main/java/com/facebook/stetho/inspector/elements/StyleAccumulator.java

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.stetho.inspector.elements;
+
+public interface StyleAccumulator {
+  void store(String name, String value, boolean isDefault);
+}

stetho/src/main/java/com/facebook/stetho/inspector/elements/android/DialogFragmentDescriptor.java

@@ -23,6 +23,7 @@
 import com.facebook.stetho.inspector.elements.Descriptor;
 import com.facebook.stetho.inspector.elements.DescriptorMap;
 import com.facebook.stetho.inspector.elements.NodeType;
+import com.facebook.stetho.inspector.elements.StyleAccumulator;
 
 import javax.annotation.Nullable;
 
@@ -125,4 +126,8 @@ public View getViewForHighlighting(Object element) {
 
     return null;
   }
+
+  @Override
+  public void getStyles(Object element, StyleAccumulator styles) {
+  }
 }