android: Fix parameter for onFinishGetBitmap in ContentReadbackHandler

The boolean parameter is not necessary as we can just use null to indicate
readback failure.

android= https://chrome-internal-review.googlesource.com/#/c/169047/
BUG=

Review URL: https://codereview.chromium.org/390933003

git-svn-id: http://src.chromium.org/svn/trunk/src/build@285609 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/findbugs_filter/findbugs_known_bugs.txt

@@ -24,5 +24,3 @@ M V EI: org.chromium.content.browser.LoadUrlParams.getPostData() may expose inte
 M M LI: Incorrect lazy initialization of static field org.chromium.chrome.browser.sync.ProfileSyncService.sSyncSetupManager in org.chromium.chrome.browser.sync.ProfileSyncService.get(Context)  At ProfileSyncService.java
 M V EI: org.chromium.android_webview.AwWebResourceResponse.getResponseHeaderNames() may expose internal representation by returning AwWebResourceResponse.mResponseHeaderNames  At AwWebResourceResponse.java
 M V EI: org.chromium.android_webview.AwWebResourceResponse.getResponseHeaderValues() may expose internal representation by returning AwWebResourceResponse.mResponseHeaderValues  At AwWebResourceResponse.java
-M C NP: Null passed for nonnull parameter of ContentReadbackHandler$GetBitmapCallback.onFinishGetBitmap(boolean, Bitmap) in org.chromium.content.browser.ContentReadbackHandler.getCompositorBitmapAsync(WindowAndroid, ContentReadbackHandler$GetBitmapCallback)  At ContentReadbackHandler.java
-M C NP: Null passed for nonnull parameter of ContentReadbackHandler$GetBitmapCallback.onFinishGetBitmap(boolean, Bitmap) in org.chromium.content.browser.ContentReadbackHandler.getContentBitmapAsync(float, Rect, ContentViewCore, ContentReadbackHandler$GetBitmapCallback)  At ContentReadbackHandler.java